I understand and share your cautioning. I literally reach out to these small projects devs and ask them about what & how they store it.

True.

Although to be fair sometimes these start out as small hobby projects and then get more professional. I don’t think https://Palette.fm had a full privacy policy in the beginning but now the guy that runs it does the thing full time It seems (and was a Google engineer previously).

Not about this services but https://palette.fm for example explicitly states they don’t store images after they’ve been processed and downloaded, and since that site is run by a former Google engineer with a reputation I don’t doubt it.