There is more to the “closed source” problem that “implemented correctly”. With end to end encryption, meta can not read the chat while it is sent through their servers. BUT the en/decryption is done by their app (Whatsapp). If you send that picture to someone else, it exists unencrypted on your and their phone, where Whatsapp could read it and send it to Meta.

Meta is completely untrustworthy, but they realized how much money they can make from metadata (who/how often/when you are chatting with), that they don’t need to see your images. HOWEVER if you send that picture in any way and either you or the receiver has tiktok, then you have to assume, the picture of your baby is now on a server in China. So don’t send that image if you do not trust the receiver to make smart choices about which apps they give permissions to