[collinmanderson]

I have a feeling PNG might work on Google Photos too, but I haven't tried it.

[binwiederhier]

If you wanna give it a shot, try the code I linked here: https://news.ycombinator.com/item?id=19916126

Although if Picasa (predecessor to Google Photos) worked with BMP, it may be better to do that because it's much easier and more space efficient to encode arbitrary data in than PNG.