This is kind off a grey area for me because i never really ask for recent pictures, i usually just ask for nudes off girls i've already seen xD
Anyways, you could do this indirectly like: "I wonder if you have nice smile", running no risk and hoping she suggests showing you a picture
Directly which would be like " I'm sure you have a cute smile, mind showing me im right?

"
Or the way i'd probably do it is be create a conversation which allows me to share one of my photos with her like: "I went to Ecuador this summer, it was pretty awesome cause i went to the hot springs, wanna see a picture?" and then send her one of mine. This will make it more likely that she will show you hers because she's seen you and you pretty much built trust/comfort by showing that exchanging pictures isn't really a big deal and you're not tryingt to get anything from her or you're not some weirdo that will jack off to her (non-nude) photos.
Hope this helped matey, take care!
