You can send photos but make sure they are G-rated. Keep in mind that he has very limited storage space for personal items so don't send a ton - I sent photos printed out on printer paper and wrote my letters around them - less bulky to store. Don't send so many at once that they don't fit in a standard envelope with standard postage.
BabyL, as NavyMum stated yes, it is fine to send photos. See Letter Writing & Fun Stuff/Questionnaires to send to your Recruit for more on that and more.
I left info for you on your My Page.