I feintly remembered reading long time ago, that FPC PNG would have some non-free licence. But now that i tried to find information, i found nothing. All FPC graphics seem to be of same modifiedLGPL that all the other code. But is FPC implementation heavier than this? Maybe it's coming at the cost of supporting more formats, i don't know. I went through all PNG related source files i could find, and there were none licence differences.