Formal:
* Des photos magnifiques: This is a classic and elegant way to say "amazing pictures."
* Des photos extraordinaires: This is a more formal and slightly stronger expression, meaning "extraordinary pictures."
Informal:
* Des photos super/géniales/extra: These are more colloquial ways to say "amazing pictures," using words like "super," "great," and "extra" which are common in everyday French.
* Des photos qui déchirent: This is a very informal and slangy way to say "amazing pictures," literally meaning "pictures that rip," but it implies something really impressive.
You can also use the verb "être" (to be) followed by an adjective like "incroyable" (incredible), "extraordinaire" (extraordinary), or "fantastique" (fantastic) to describe the pictures:
* Ces photos sont incroyables! (These pictures are incredible!)
* Les photos sont extraordinaires! (The pictures are extraordinary!)
* Les photos sont fantastiques! (The pictures are fantastic!)
The best way to choose the right phrase depends on the situation and your relationship with the person you are talking to.