I'm really liking the color interactions...and I think this will be nice whether or not its photographic. The textures of fur are hard to do...I drew my dogs snout for my first computer painting, and I had a hard time with it. I like what you're doing though compositionally. I'm no expert, but if you could some how make the dogs lips a little more subtle, it might just give it that real sense.
My advice to you with realism would be to avoid generalizing details. I know that sounds rather awkward so I'll explain it for ya. Here's an example, when drawing realism, you're gonna need to use different brush sizes for the details within the picture. Seems to me that you have the same line weight going all around him here. Take a good look at the reference, and choose a brush that best suits the detail you want to work out. If it's fur, I can definitely see you using even a 0 pixel brush (I dunno how it exists, but it's the thinnest you can work with), especially if the fur isn't pitch black or has no real depth/contrast. Try analyzing the area you're looking at in the reference and break them down into shapes in your head. Once you've done that, put it back down onto your drawing. If you can get accurate with even the smallest of shapes within details, your picture will look more accurate and in this case even help it look more real...good luck with that.
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You own realism better than me. Not right XD