This is a small How-To on changing the background color of a image to transparent using open source GIMP Image editing application. The idea is to add alpha channel, select by color and cut it. Let me put it in detail here.
Step-1: Open the Image in GIMP.
Step-2: Navigate Layer -> Transparency -> Add Alpha Channel.
Step-3: Navigate Select -> By Color
Step-4: Mouse click on background color of image
Step-5: Navigate Edit -> Cut.
Step-6: Save it in format of your choice (Warning: JPEG does not support transparency, so opted for PNG format).