I know a decent number of the smaller publishers in our hobby, and I'm constantly reminded that one of the biggest expenses in getting any product out isn't the writing, but the art. Getting original pieces of art made for your project can be cost prohibitive, thus the use of stock art.
With stock art, you license the use of the art for use in your projects but others may also do the same. You license isn't exclusive - others may also use the art in their projects, but the price is generally much more affordable then getting artwork made specifically for your project.
Inkwell Designs has a large amount of high quality monster stock art for sale at RPGNow, and they even have their Ogre Stock Art available for free for you to use in your projects. Can't beat that.
The Minotaur for Old-School Essentials
*Requirements:* Minimum STR 9, Minimum CON 9
*Prime Requisite:* STR and CON
*Hit Dice:* 1d10
*Maximum Level:* 8
*Armor:* Leather, including shield...