Formal:
* Gostou da foto? (Did you like the picture?) - This is the most direct and neutral way to ask.
* O que achou da foto? (What did you think of the picture?) - This is a more polite and open-ended way to ask for an opinion.
Informal:
* Curtiu a foto? (Did you like the picture?) - This is a more casual way to ask, similar to "like" in English.
* E aí, gostou da foto? (Hey, did you like the picture?) - This is even more informal and can be used with friends or close acquaintances.
The best way to say it depends on the situation and your relationship with the person you are speaking to.