diff --git a/include/exiv2/ini.hpp b/include/exiv2/ini.hpp
index b3b1c9b0..c1749a3b 100755
--- a/include/exiv2/ini.hpp
+++ b/include/exiv2/ini.hpp
@@ -175,8 +175,7 @@ public:
 
       @return value
     */
-    std::string Get(std::string section, std::string name,
-                    std::string default_value);
+    std::string Get(const std::string& section, const std::string& name, const std::string& default_value);
 
     /*! @brief Get an integer (long) value from INI file, returning default_value if
         not found or not a valid integer (decimal "1234", "-1234", or hex "0x4d2").
@@ -187,7 +186,7 @@ public:
 
       @return value
     */
-    long GetInteger(std::string section, std::string name, long default_value);
+    long GetInteger(const std::string& section, const std::string& name, long default_value);
 
     /*! @brief Get a real (floating point double) value from INI file, returning
         default_value if not found or not a valid floating point value
@@ -199,7 +198,7 @@ public:
 
       @return value
     */
-    double GetReal(std::string section, std::string name, double default_value);
+    double GetReal(const std::string& section, const std::string& name, double default_value);
 
     /*! @brief Get a boolean value from INI file, returning default_value if not found or if
         not a valid true/false value. Valid true values are "true", "yes", "on", "1",
@@ -211,12 +210,13 @@ public:
 
       @return value
     */
-    bool GetBoolean(std::string section, std::string name, bool default_value);
+    bool GetBoolean(const std::string& section, const std::string& name, bool default_value);
 
 private:
     int _error;                                                        //!< status
     std::map<std::string, std::string> _values;                        //!< values from file
-    static std::string MakeKey(std::string section, std::string name); //!< return key encoded from section/name
+    static std::string MakeKey(const std::string& section,
+                               const std::string& name);  //!< return key encoded from section/name
     static int ValueHandler(void* user, const char* section, const char* name,
                             const char* value); //!< value handler
 };
diff --git a/samples/Jzon.cpp b/samples/Jzon.cpp
index 0c150969..76890fb2 100644
--- a/samples/Jzon.cpp
+++ b/samples/Jzon.cpp
@@ -458,7 +458,7 @@ namespace Jzon
     {
         children.push_back(NamedNodePtr(name, node.GetCopy()));
     }
-    void Object::Add(const std::string &name, Value node)
+    void Object::Add(const std::string &name, const Value &node)
     {
         children.push_back(NamedNodePtr(name, new Value(node)));
     }
@@ -570,7 +570,7 @@ namespace Jzon
     {
         children.push_back(node.GetCopy());
     }
-    void Array::Add(Value node)
+    void Array::Add(const Value &node)
     {
         children.push_back(new Value(node));
     }
diff --git a/samples/Jzon.h b/samples/Jzon.h
index b784c320..d8230ce9 100644
--- a/samples/Jzon.h
+++ b/samples/Jzon.h
@@ -251,9 +251,9 @@ namespace Jzon
         Type GetType() const override;
 
         void Add(const std::string &name, Node &node);
-		void Add(const std::string &name, Value node);
-		void Remove(const std::string &name);
-		void Clear();
+        void Add(const std::string &name, const Value &node);
+        void Remove(const std::string &name);
+        void Clear();
 
 		iterator begin();
 		const_iterator begin() const;
@@ -319,9 +319,9 @@ namespace Jzon
         Type GetType() const override;
 
         void Add(Node &node);
-		void Add(Value node);
-		void Remove(size_t index);
-		void Clear();
+        void Add(const Value &node);
+        void Remove(size_t index);
+        void Clear();
 
 		iterator begin();
 		const_iterator begin() const;
diff --git a/samples/exiv2json.cpp b/samples/exiv2json.cpp
index 968038ff..4bf8584c 100644
--- a/samples/exiv2json.cpp
+++ b/samples/exiv2json.cpp
@@ -91,7 +91,7 @@ bool getToken(std::string& in,Token& token, std::set<std::string>* pNS=NULL)
     return result;
 }
 
-Jzon::Node& addToTree(Jzon::Node& r1,Token token)
+Jzon::Node& addToTree(Jzon::Node& r1, const Token& token)
 {
     Jzon::Object object ;
     Jzon::Array  array  ;
diff --git a/samples/geotag.cpp b/samples/geotag.cpp
index 5fa5a726..417291bc 100644
--- a/samples/geotag.cpp
+++ b/samples/geotag.cpp
@@ -670,7 +670,7 @@ bool sina(const char* s,const char** a)
     return bResult;
 }
 
-int readFile(const char* path,Options /* options */)
+int readFile(const char* path, const Options& /* options */)
 {
     FILE* f     = fopen(path,"r");
     int nResult = f ? typeFile : typeUnknown;
diff --git a/samples/key-test.cpp b/samples/key-test.cpp
index 4eb43459..6922a96d 100644
--- a/samples/key-test.cpp
+++ b/samples/key-test.cpp
@@ -87,7 +87,7 @@ int main()
     // -----
 
     // Copy constructor
-    ExifKey ek2(ek);
+    const ExifKey& ek2(ek);
 
     // operator<<
     tc += 1;
diff --git a/samples/taglist.cpp b/samples/taglist.cpp
index 683c75c8..ed6a0e18 100644
--- a/samples/taglist.cpp
+++ b/samples/taglist.cpp
@@ -68,8 +68,7 @@ int main(int argc, char* argv[])
                             std::istringstream input(tags.str()) ;
                             while (std::getline(input, line)) {
                                 std::cout << groupList->groupName_ << "."
-                                          << (item == "all" ? line.substr(0,line.find(",")) : line)
-                                          << std::endl;
+                                          << (item == "all" ? line.substr(0, line.find(',')) : line) << std::endl;
                             }
                             groupList++;
                         }
diff --git a/src/actions.cpp b/src/actions.cpp
index b886a12c..536b80af 100644
--- a/src/actions.cpp
+++ b/src/actions.cpp
@@ -150,7 +150,7 @@ namespace {
              with
              os << make_pair( myString, width)
      */
-    std::ostream& operator<<( std::ostream& os, std::pair<std::string, int> strAndWidth);
+    std::ostream& operator<<(std::ostream& os, const std::pair<std::string, int>& strAndWidth);
 
     //! Print image Structure information
     int printStructure(std::ostream& out, Exiv2::PrintStructureOption option, const std::string &path);
@@ -2175,7 +2175,7 @@ namespace {
         return 0;
     }
 
-    std::ostream& operator<<( std::ostream& os, std::pair<std::string, int> strAndWidth)
+    std::ostream& operator<<(std::ostream& os, const std::pair<std::string, int>& strAndWidth)
     {
       const std::string& str( strAndWidth.first);
       size_t minChCount( strAndWidth.second);
diff --git a/src/ini.cpp b/src/ini.cpp
index bea9e080..7b66f441 100755
--- a/src/ini.cpp
+++ b/src/ini.cpp
@@ -238,13 +238,13 @@ int INIReader::ParseError() const
     return _error;
 }
 
-string INIReader::Get(string section, string name, string default_value)
+string INIReader::Get(const string& section, const string& name, const string& default_value)
 {
     string key = MakeKey(section, name);
     return _values.count(key) ? _values[key] : default_value;
 }
 
-long INIReader::GetInteger(string section, string name, long default_value)
+long INIReader::GetInteger(const string& section, const string& name, long default_value)
 {
     string valstr = Get(section, name, "");
     const char* value = valstr.c_str();
@@ -254,7 +254,7 @@ long INIReader::GetInteger(string section, string name, long default_value)
     return end > value ? n : default_value;
 }
 
-double INIReader::GetReal(string section, string name, double default_value)
+double INIReader::GetReal(const string& section, const string& name, double default_value)
 {
     string valstr = Get(section, name, "");
     const char* value = valstr.c_str();
@@ -263,7 +263,7 @@ double INIReader::GetReal(string section, string name, double default_value)
     return end > value ? n : default_value;
 }
 
-bool INIReader::GetBoolean(string section, string name, bool default_value)
+bool INIReader::GetBoolean(const string& section, const string& name, bool default_value)
 {
     string valstr = Get(section, name, "");
     // Convert to lower case to make string comparisons case-insensitive
@@ -275,7 +275,7 @@ bool INIReader::GetBoolean(string section, string name, bool default_value)
     return default_value;
 }
 
-string INIReader::MakeKey(string section, string name)
+string INIReader::MakeKey(const string& section, const string& name)
 {
     string key = section + "=" + name;
     // Convert to lower case to make section/name lookups case-insensitive
diff --git a/src/pngchunk_int.cpp b/src/pngchunk_int.cpp
index 81c70886..42e61ba0 100644
--- a/src/pngchunk_int.cpp
+++ b/src/pngchunk_int.cpp
@@ -240,10 +240,7 @@ namespace Exiv2 {
 
     } // PngChunk::parsePngChunk
 
-    void PngChunk::parseChunkContent(      Image*  pImage,
-                                     const byte*   key,
-                                           long    keySize,
-                                     const DataBuf arr)
+    void PngChunk::parseChunkContent(Image* pImage, const byte* key, long keySize, const DataBuf& arr)
     {
         // We look if an ImageMagick EXIF raw profile exist.
 
diff --git a/src/pngchunk_int.hpp b/src/pngchunk_int.hpp
index 4901dc7a..018eae67 100644
--- a/src/pngchunk_int.hpp
+++ b/src/pngchunk_int.hpp
@@ -131,10 +131,7 @@ namespace Exiv2 {
                     Xmp  packet generated by Adobe                 ==> Image Xmp metadata.
                     Description string                             ==> Image Comments.
          */
-        static void parseChunkContent(      Image*  pImage,
-                                      const byte*   key,
-                                            long    keySize,
-                                      const DataBuf arr);
+        static void parseChunkContent(Image* pImage, const byte* key, long keySize, const DataBuf& arr);
 
         /*!
           @brief Return a compressed (zTXt) or uncompressed (tEXt) PNG ASCII text chunk
diff --git a/src/xmpsidecar.cpp b/src/xmpsidecar.cpp
index 5d6a4326..4a71ae3a 100644
--- a/src/xmpsidecar.cpp
+++ b/src/xmpsidecar.cpp
@@ -119,7 +119,7 @@ namespace Exiv2 {
         return b;
     }
 
-    static bool matchi(const std::string key,const char* substr)
+    static bool matchi(const std::string& key, const char* substr)
     {
         return toLowerCase(key).find(substr) != std::string::npos;
     }
diff --git a/unitTests/test_XmpKey.cpp b/unitTests/test_XmpKey.cpp
index f2ebe26a..f204c24d 100644
--- a/unitTests/test_XmpKey.cpp
+++ b/unitTests/test_XmpKey.cpp
@@ -75,7 +75,7 @@ TEST_F(AXmpKey, correctlyInstantiatedWithValidPrefixAndProperty)
 TEST_F(AXmpKey, canBeCopiedConstructed)
 {
     XmpKey key(expectedPrefix, expectedProperty);
-    XmpKey copiedKey(key);
+    const XmpKey& copiedKey(key);
     checkValidity(copiedKey);
 }