There are two types of art assets used in this engine: sprites and sprite sheets.

Sprites

This is your basic static image.  It has an arbitrary position and orientation in world coordinates, scaling factors along the original X and Y axis, and a color modification.

Sprite Sheets

Sprite sheets have all the same parameters sprites have, however they are a series of sprites that are cycled on an interval.  The source image must contain all sprites to be incorporated in a uniformly sized grid.