Well, I'll stick my neck out and might not be happy about what I hear, but I'll try to remind myself of that while reading the answers ;)
In the photo below I concider my horse to be fairly collected. I'm ''just'' a trailrider and he is ''just'' an off the track, gaited standardbred. I ride him in flatwalk, rack and sometimes trot (walk and canter of course) but in the picture he's doing a sort of gaited gait. He's moving forward in a slow manner and he's having a clear 4-beat (this I can hear and feel, but it was a bit on the diagonal, trotty side, rather than completely square or lateral/pacy). He's moving forward on a straight line.
It's a bad quality cellphone photo, I've removed the background (a road and some trees) and changed the levels/colors, but not altered it otherwise. I would love a better or more photos, but the truth is I can usually only get this from him when I'm alone on the trail and have bee working him properly for a good while. When I have company, I have diffiulties working and focusing on the horse as I like to chat with my friend on the ride, and therefore I rarely get pictures or even eyewitnesses when we do these kind of things. I was lucky this day though :) Hopefully soon I can get this mre often and easier as we get better.
Would you say he's fairly collected, and what in his body etc tells you he is or isn't? (I know my heels are op.. >_>)
Perhaps it's easier if you compare with a ''natural'' photo of him, I mean... it might be easier to see how he has changed his frame if you know how it's normally.. a heavy, short backed horse might give a different impression than a lean, longbacked one, if you see what I try to say.. can't hurt at least...
(and for those suspicious of any kind of edited photos, here's the original: http://www.elftown.com/stuff/12062011090.jpg )