Trying to work out what app or site this picture was taken from.

The top right depicts that it is a snap chat file. If this is a saved file (I assume you're not lying and you didn't accidentally receive that snap at that time or you would know the app).

Originally with the snap chat application one could save a picture of the 10 second view of a picture sent through the application. Now a days that has been updated to not work so people take on other methods.

He either received this a long while back and is saved or was within the phones time of use had a picture saved from one of the online sites with many of these pictures I believe there is one specifically for this purpose as well, safe to assume that possibility.

To end it is a picture on a phone from someone most likely no longer in his life. Drink some wine, cook him a dinner, and fuck his brains out. You'll be fine.