A poor man's straightening tool that helps you validate that you have got it level simply uses the window the image is displayed in to check it. After straightening all you do is use the window resize handles to narrow the view until the top or botom display begins at the horizon. That makes it easy to see if it is level. It can be used for vertical checking to.
I use it during voting to quickly validate if an image is level or not. I also use window resizing during voting to try different "crops" on images to see if they look better.
I'd be careful with Picasa... it will save your image without telling you and that is highly undesireable. If you are looking at an original you don't want modified you may be unaware you changed it.
Does Picasa straighten dq you from basic editing? OR is it considered part of the croping process?
It's not the straightening, it's whether you accidentally save over your original, then it's no longer "unaltered" and your image can't be validated as legal. If I were using Picasa, I'd drag a copy of my original to a new folder on my HD before I even OPENED it in Picasa...
