Picture in iPhone Signature

Has anyone figured out how to add a picture to a signature in an iPhone email? I have changed the size, tried with jpeg and png, tried copying and pasting from a new email, tried copying and pasting from photos, tried copying and pasting from an old email, tried copying and pasting from Notes... Seriously this can't be that difficult. Bonus points if we can add a link to the picture in question, but that might be asking too much.

I have an iphone 12 mini, but I tried on my boss's iPad and having as much luck.

Many thanks, friends.