ImageGear provides the  Annotation API: ART component for working with annotations.

ImageGear ART Component

The ImageGear ART component includes low-level functions for fine-tune image annotating and high-level functions for the most typical operations. ART creates annotations on a layer that sits above the image or document that is to be annotated. The original image and the annotations can be stored separately or merged together permanently. See Annotation API: ART for information about using the ART Component.