I thought you mean downloading the graphic. Sorry, my mistake
What you need/mean is graphic transparency.
there are different graphic file types, depending on purpose (
very important in html/website programming):
.svg, .png, .gif supports transparency
.bmp, .jpg do not.
I'm using
paint.net and with enclosed tool "Magic Wand", you can select a specific color/area, delete it and get a transparent background. See enclosed file : transparency.png
with smooth and soft filter, you would get a passable picture. See enclosed file : transparency_soft-filter.png
with paint.net you can add layer (like different foil for overhead projector). See enclosed file : transparency_new_background-color.pdn
paint.net magic wand tutorial