XnView Shell Extension

XnShell is a practical Windows Explorer extension which allows you to edit and convert images just by right-clicking them.

This app integrates with your system to put basic photo conversion tools at your fingertips, including the ability to change the format, resolution or rotation of the image, as well as the ability to set them as your desktop wallpaper or upload them directly to ImageShack.

XnShell is a great way to quickly and easily make changes to your photographs, because you can make all of the edits with just one click. Do you need your JPEG image in PNG format? Just access the XnShell option from Windows Explorer and it will be ready. In addition, the program supports GIF, BMP, JPG, PCX, PNG, TIF and TGA extensions.

A good feature of this extension is that you can convert your images in batches, which keeps you from having to repeat the same processes with each individual image.