I don't know the answer, but for what it's worth it won't be a DLL file. DLL stands for "Dynamic Link Library", and they contain the code that you need to run the program (and yes, occasionally the odd picture or two, but they're compiled in). The pictures may well be stored in a binary type file (which means that you won't be able to open them easily) but it would probably be called something other than DLL, like DAT or RES or something like that.
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