How are multiple-image operations like watermarks and blends charged?

Images that are used as overlays, watermarks, etc. will count as master images even if they are not addressed or served directly. For example, if you have 5 images of cars and 1 image of a logo, and you use the logo as a watermark on each of the car photos, you would be billed for 6 master images. The logo image may never be delivered directly, but still counts as an master image since it is fetched to render the logo watermark.