If you're good at IUPAC naming conventions, it is possible to easily identify the difference between these similar molecules. But if it's been a while since you've done organic chemistry, this will work--if you have acrobatic eyes.
Look at the figure above and go cross eyed, such that the two structures overlap. Once they are close, you will find that tilting your head slightly right or left will allow the images to completely lock-on. Then inspect the superimposed image, some part will seem to flicker, or just seem not quite as solid as the rest. That is the place with a difference. Try it.
It is the double bond in the top left of the right-most ring. The left image has it and the right one doesn't.
The original, slightly better image is here.
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