SageThumbs is a powerful application that adds an image thumbnail in the right-click context menu of the Windows File Explorer. The application is powered by the GFL library of Pierre-e Gougelet who has also created the popular XnView picture viewer. In addition to showing the thumbnail previews, SageThumbs also allows you to convert images from one format to another.
SageThumbs is an open source application for Windows and can be downloaded from its Google Code webpage. The download comes as a setup installer. After the installation, it shows all the image files in Windows File Explorer as thumbnails. Even if you choose to display all the file as icons, SageThumbs forces Explorer to use the image thumbs as icons. Now when you right-click on any type of image file in Windows, you would see a new context menu item SageThumbs, selecting upon which it shows a small thumbnail preview of the selected image.
In the same menu, you would find many other options like setting the image as your Windows desktop wallpaper (background), sending the image or its thumbnail by email, and converting the image to JPG, BMP, GIF or PNG formats. You can also open the SageThumbs settings, by selecting SageThumbs Options from this same menu.
In the settings, you can enable/disable displaying of the thumbnails in the context-menu, show thumbnails in Explorer, display thumbnails as icons, set context menu thumbnail preview size (by default it is 256×256 pixels), select image conversion options for JPEG and PNG files, set thumbnail cache size, select/unselect supported image file types for which context menu thumbnail is displayed, and more.
SageThumbs supports dozens of image file formats, but if you want to display the context menu thumbnails for the AI (Adobe Illustrator files), PDF, PS and EPS files, then you will have to install GhostScript on your system. GhostScript is a free software that you can download from www.ghostscript.com.
If you have an older PC, then you may want to turn off displaying of the thumbnails in the Windows Explorer. With SageThumbs installed, this can be a little tricky. In addition to disabling the thumbnails in the File Explorer, you have to uncheck both the checkboxes labeled Enable thumbnails in Explorer and Use thumbnails as icons in Explorer in the SageThumbs settings.
You can download SageThumbs from http://code.google.com/p/sagethumbs/.