jpeg

TJPEGData is used for the internal implementation of TJPEGImage. TJPEGData is created automatically by the TJPEGImage object when that image object is created. 

TJPEGData owns the file handle to the jpeg data source. Thus, TJPEGData implements how TJPEGImage does reference counting and handle sharing. When a jpeg image object is copied using the Assign method, those multiple instances of the image object refer to the same TJPEGData object. 

The TJPEGData file itself is never modified. Each TJPEGImage instance that shares it has its own properties that determine how this data is decompressed into its own internal, local bitmap representation. However, if a TJPEGImage needs to modify the actual jpeg data, it breaks its link to that particular TJPEGData instance and creates a new one. 

TJPEGImage 

TJPEGImage