It looks like 90% of the watermelons out there. If it were any other color or pattern, it might be easier. I'm no expert though, but I doubt even an expert could really identify it. You can't even tell what color the flesh will be from that picture.

While it's nearly impossible to be definite with so many varieties out there, I'd say it is of the Crimson Sweet type.

Yes, I agree with brookw, Crimson Sweet does look like that, and it is a very popular (and desirable) one. A few others I know of that can look similar at that stage are: Kolb's Gem, Georgia Rattlesnake, Daisy, and Orangeglo, but none of these are too common.

Does this pic help?