Is used by Mac OS installers. It contains a list of files to install, their size and a checksum of the contents. The installer can compare this with the files already on the system, and decide what to do. You find BOM files inside of the installer packages, and inside the receipts file which gets stored in the /Library/Receipts folder.
To see the contents of a "Archive.bom" drop it on File Juicer and look in the folder for extracted text files.
As bom files has a list of files it refers to File Juicer will follow this list and process them too. It can generate an index of the files found so you can see the images imstalled.
Apple about the bom format
About the lsbom command