I was considering that too, but damselfly nymphs have large visible exposed gills at the tips of their tails (look like feathers) which don't seem to be present here.
Some dragonflies have short, squat nymphs but many others are built like this one. It's still pretty bulky compared to a typical damselfly nymph, which is very slender and petite in appearance. I think it's a dragon...
Honestly, either way, these critters are truly amazing to watch in an aquarium as they progress through their development. Not a great choice for a community of small fish, but well worth giving giving a small tank to for a summer.
Google some info about their prey-capture adaptations and methods. The stuff is straight out of the movie "Alien".