If you are actually in the image and it is clear that you are in the picture, then you might simply say
That's me!
If it is clearly you in the picture, but you are doing something that you think is typical of you—like if you are a goofy person, and you are making a funny face in the picture—then you would say
That is so me!
If there is some doubt that you are actually in the picture, but you are confident that it is you, then you might say
That is so me!
If you see a person in a picture, and it is clearly not you, but you think the person represents you— like your looks, or your personality, or something like that—then you could also say
That's so me!.
I believe that in each instance, this and that are likely to be interchangeable.