Great question, Deepak! They are both grammatically correct, but have different meanings, as there are different kinds of possession. A photo of you is a photo in which you appear — you are in the photo. A photo of yours is a photo that you own — the subject could be anybody, or anything. Alternatively, “your photo” would be ambiguous as to whether you are in the photo or whether you own the photo (and would usually be considered definite, rather than indefinite). In the example you gave, it is probably “this one of you”.

"Pity" is "a feeling of sadness or sympathy for someone else's unhappiness or difficult situation". When we describe something as "shame", it is something that "is disappointing or not satisfactory". It can also mean "an uncomfortable feeling of guilt or of being ashamed because of your own or someone else's bad behavior". As far as I'm aware "it's a shame" and "it's a pity" are interchangeable. Just remember that shame and pity have slightly different meanings, though. (the definitions aren't my own, but are from the Cambridge dictionary)

This one of YOU ( not “yours”)

Also, your sentence is fine. Alternatively you could say something like, "I found a photo of you when I was looking through the old photos on my phone". (sorry again for the mix-up)

Yours is a pronoun, it used to refer to a thing or belonging to someone. Your sentence is correct if the photo belongs to the person. If the photo is of the person you would rather say: "I was looking through some old photos on my phone and I found this one of you"