Hi, I think the dog might be a Great Dane. The dog "Scooby Doo" in the cartoon is actually a Great Dane. Is this how the dog looks like? Some of these dogs' ears can be altered so they appear to stand straight:
Great Dane (Deutsche Dogge, German Mastiff)
I think he's right. Although the dog isn't as young as the dog in the photo above, its long hind legs sure reminded me of Scooby's.