I use gimp to edit or create images. Lately I got an email asking: how can I change the background color an images, so it can better blend on any background on my web page? I would change the color to transparent rather than a specific color and here is how I would do it:
If you don’t have Gimp, download it from here. It’s a high quality image manipulation software that you can download under the GNU license.
Open the image in Gimp
From the Layer menu item, click on Transparency and then click on the “Add Alpha Channel” the first item in the submenu.
Click on the fuzzy selection tool from the Toolbox panel and highlight the background area on your image that you want to make transparent.
Click on the “delete” button on your laptop, or select the menu item “clear” under the Edit menu. You will start seeing the background color change to transparent. Shown in the software as gray squares (see image below).
Now you can save the new image and you should be done.