Feel free to give these "Freeware" simple ones a try. One is bound to do the job you need. There are many more, like Photoshop or even Paint or PaintNet as well that have much more capability.
Thank you for the suggestions. I do use Photoshop CS and have several of the freeware programs you mention.
I don't think I framed my question well, so let me give it another try.
I'm talking about the native format of the N7 screenshots, which is .png. PNG, like GIF, is great for line art and text; JPEG is better for capturing the subtle gradations found in photographs.
I was just wondering if I had the option of saving an image to a .jpg when taking a screenshot of a photo with the N7. Or is the .png format the only choice for screenshots?
I am trying to avoid having to convert a .png to a .jpg.