JEITA  CP-3451 - 11 - 4.5.4   Basic Structure of JPEG Compressed Data Compressed data files are recorded in conformance with the JPEG DCT format specified in ISO/IEC 10918-1, with the Application Market Segment (APP1) inserted. APP1 is recorded immediately after the SOI marker indicating the beginning of the file (see Figure 6). Multiple APP2 may be recorded as necessary, starting immediately after APP1. APPn  other  than  APP1  and  APP2  or  COM  segments  are  not  used  by  Exif.  However  Exif  readers  should  be designed skip over unknown APPn and COM. Figure 6 Basic Structure of Compressed Data Files   Interoperability, APP1 consists of the APP1 marker, Exif identifier code, and the attribute information itself. The size of APP1 including all these elements shall not exceed the 64 Kbytes specified in the JPEG standard. Attribute information is stored in TIFF structure including a File Header, with a maximum of two IFD (0th IFD, 1st IFD). The 0th IFD records attribute information concerning the compressed image (primary image). The 1st IFD may be used to record a thumbnail image. For details see section 4.7.2. APP2 consists of the APP2 marker, FPXR (Flashpix Ready) identifier code, and contents list for Flashpix extension recording, or stream data. A string of multiple APP2 marker segments may be used to record data exceeding 64 Kbytes. For details see section 4.7.3. APP1 Application Marker Segment 1 (Exif Attribute Information) SOI Start of Image DQT Quantization Table DHT Huffman Table SOF Frame Header SOS Scan Header Compressed Data EOI End of Image APP1 Marker APP1 Length Exif Identifier Code TIFF Header 0th IFD 0th IFD Value 1st IFD 1st IFD Value 1st IFD Image Data Structure of Compressed file Structure of APP1 (DRI) (Restart Interval) (APP2) (Application Marker Segment 2) (FlashPix Extension data)