Chris--both good points.
is there a way to hold a fish with one hand that's not injurious to it or me?
Casey, sounds like you got the old bloody-thumb-from-holding-trout-like-bass thing! Sometimes a trout will relax when cradled gently under the belly, sometimes not. Regardless, the picture that results is often lousy. (I know whereof I speak; I've taken lots of lousy fish pictures.) Here's what I'd recommend:
Whenever you realize that you've hooked a fish you
must capture photographically (and that you might actually land), start looking for a shallow spot near shore where it's possible for the fish to be on its side but still partially submerged (an inch or so of water). After netting the fish and removing the hook (in the water), lay the fish in the net in that spot. (You can lay your rod alongside--mostly just to get it out of the way, but it also adds perspective). Work quickly to snap a shot or two, then hold the fish upright in flowing water until it swims away. If any complications arise that might cause unacceptable delays, abandon the effort and release the fish. Flopping that might injure the fish can usually be prevented by covering the fish's eye while you ready the shot.
A few provisos:
1. If you can't see such a spot, if the fight has been unusually long, or ESPECIALLY IF THE WATER IS WARM, abandon the photo idea, revive the fish carefully, and live with the memory. (When the water is very warm, you probably shouldn't be fishing for trout anyway.)
2. If your first or second shot is lousy, you can carefully turn the fish over so the other set of gills is in the water and snap another. (But don't get carried away; discretion is the better part of fish photography.)
3. Some consider it egotistical to want to get pictures of fish (and it is, I suppose), but I would also point everyone to David's (DMM's)
excellent post in the "Catch and Release" thread (in the general section). I have great faith in what he says there, and it matches my experience.