Create the image you want in, say, Photoshop or Paint Shop Pro, don't make it larger than 500x125 pixels. Save it as a .jpg or .gif, and upload it to an image hosting site, or here:
"Stephen Wolfram is the creator of Mathematica and is widely regarded as the most important innovator in scientific and technical computing today." - Stephen Wolfram
"Stephen Wolfram is the creator of Mathematica and is widely regarded as the most important innovator in scientific and technical computing today." - Stephen Wolfram