Thank you very much Neil. I always experience difficulties with to and for.

Hello,
how are you my name is miss Naarah , I'm single never married, and its my pleasure to write you as well, can i be your friend,reply my mail please do not for get,([email protected])

Both "to" and "for" are possible.  However, in your particular situation, "for" is better.  "Could you come up with a caption for this photo?"         ["for" indicates the beneficiary (the thing which will get a benefit).  In this case, the photo will get a benefit -- the caption.]

But sometimes "to" would sound better:  "Could you add a caption to this photo?"    "Without my glasses, I can't read the caption to this photo."