And this is ONLY my opinion, not a for sure way to know...
Not that long ago we purchased a Jungle as well, There are a few things I personally look for in a jungle, but that doesn't mean they are tell tale signs of a Jungle.
1- Its hard to explain, but many jungles have a sooty, almost darker color on thier sides, while the dorsal (top) part is squeeky clean (Or really noticably cleaner), and you can almost see the line where the Clean top meets the dirtier sides...

2- Aberrant pattern, Many don't have any abbarencies, which makes it harder, but even on the little to no abbarency ones, the saddles tend to have this big HOLE in the middle of them....Maybe some Saddles are connected...stretched out...Any Abberancy is good....

My Jungle was born 2/11/08 so she is almost 6 months old now....they tend to gain beautiful color as they grow.....Here she was before I got her...
Photo belongs to dbBoas.com

These things are by NO MEANS a for sure way to tell, but its things I noticed when I saw pics of Jungles, Most importantly knowning that one of the parents was an actual real Jungle is key, with mine, the father that produced her was purchased from Peter Kahl...and is a Swedish Jungle.
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Executive Reptiles
Amanda Kingsbury & David Kendrick
www.executivereptiles.com