Below is an example of the ExifTool HtmlDump output (the exiftool '-htmlDump' option). Move your cursor over the data to highlight individual blocks and reveal tool tips for extra information. (You must have JavaScript enabled.)
Normal data blocks are light or dark green, unused blocks are yellow, and double-referenced blocks are red or pink. A blue tag name indicates the value is referenced by an offset in the IFD (ie. the value is longer than 4 bytes), and a purple name indicates that the actual offset differs from the recorded offset. All data in the maker notes value block is underlined.
Currently, only TIFF/EXIF and JPEG meta information is dumped. By default, all offsets are relative to the start of the TIFF header (as below). For a TIFF image this is at the start of the file, but for a JPEG image it is 6 bytes into the APP1 EXIF segment. However, this base offset can be specified on the command line with '-htmlDump#' (ie. '-htmlDump0' for absolute offsets), or via the API with the 'HtmlDumpBase' option.