Ha, "base64 encoded PNGs"? This is so bizarre, i had to look it up!
So this is likely about "data URI" data:image/png;base64, used to embed small images in HTML/CSS as in:
9TXL0Y4OHwAAAABJRU5ErkJggg==" alt="Red dot" />
It beggars belief someone would actually store
single images in base64 (since either the entire composed CSS would be kept on CDN for speed or base64-being-so-fast would be done on the fly). Worst case (extracting from a composite file), renojim's applies - otherwise RokuKC's.