Maybe they think you don't like taking selfies or pictures? You said you don't have Instagram or Snapchat, I assume they know you don't... they may just be guessing that you don't want to, instead of asking.

Awhile back, I never used to hang out with people outside of certain circumstances. Tfhey had all gotten so used to it, that I never got invited anymore. It's not that I wasn't invited, they just didn't ask because my answer had been no for so long. The first time I wanted to go, I was nervous cuz my head told me they didn't want me there since they never asked... but I stepped up and asked where they were going, and they told me where and then excitedly asked me "are you gonna come?"

Maybe, if you want to take a picture with them, just ask... I would probably say something like "hey, I really like how my hair came out today, can we do a picture together?" For me, without that first part, it would feel awkward. I don't know if it would for you tho, like if they would ask why today, kind of...