The Mac File structure is different from the PC file structure in that resource files are not seperate files as they are on the PC (.rsr files), but are included in the data file. Within the file header is a resource fork which directs the Mac OS to look to a seperate portion of the file for any resources (ie thumbnails for .cr2 files). I know of no PC utility which will rebuild a PC file to accomodate this structure (and combine the two files). As previously mentioned, Mac Converter will do this easily (on a Mac), so there is no need for you to do it from your PC. Just mention, somewhere in your documentation, that Mac users should convert your files using Mac Converter before attempting to use them and indicate "Mac/PC" under platforms supported. If you really want to write a utility to do this, contact MartinC and ask him if he will help you (I don't know that he will, but he is the author of Mac Converter). Jim Moore