TherioSoft is a freeware program which you can capture your screen and convert images in 4 types: PNG, JPEG, GIF, and BMP. TherioSoft is the new version of TherioImageStudio 2.
Beautiful interface - I love free software - www.ilovefreesoftware.com
A simple and intuitive application - Softpedia - www.softpedia.com
It is a lightweight software - List of freware -www.listoffreeware.com