If you are doing a demonstration, tutorial or computer based video that requires detailed screen images you should take a look at Gadwin PrintScreen.
I've seen a lot of tutorial videos that really could have benefited from using a large photo or screen shot to demonstrate a task or software feature. With a touch of pan/zoom you can make a tutorial video much easier to understand.
For computer based screen captures it works great. The free version will do everything you need but the Pro version will let you add annotations, shapes, call outs and other stuff.
There is a lot of malware web sites around so I'd suggest that you get it directly from the Gadwin web site. Sorry Mac Users, it is Windows only.