Feel free to use it for whatever purpose.
If you want better, high-quality creatures for your games, or products, check out:
For publishers: Publishing rights and original artwork
For artists: Step-by-steps, and tutorials
For game-masters: RPG-adapted stats and descriptions
For creature fans: Lots of nice critters
If the resolution of this one (above) is enough for you to print a book, you can use this creature. If you want high-resolution artwork you will have to buy it from me.
If you refer to the MonstersByEmail creatures, now available in Creature Collection 1 and Creature Collection 2, at MonstersByEmail.com they cannot be used for covers, unless you specifically purchase the rights to put them on a cover.