I use the clipping tool in Evernote - we use Evernote at work to do planning and keep notes/etc. across several computers in remote locations, so I have it installed on every machine/iPad I own and it has a built-in clipper function as well.

Anything that lets you grab a part or all of the screen will work. You just have to touch up the picture in the software of your choice (GIMP is free, so it's a good choice )