Microstock (Also Known As Clip Art) is an entire industry of Cartoonists and Illustrators, in their home studios, drawing, digitizing (inputting them into a computer) and vectorizing them, producing their illustrations to sell to Advertising Agencies, Graphic Design firms and small businesses, to enhance publications, textiles (clothing, such as tee shirts, etc.) and other print media and products. 

Here are some of my favorites: