FEATURED WEB TUTORIAL: CLEANING
Cleaning Your Sensor
Published by: bythom
This article applies to all Nikon-based digital SLR bodies (D1, D1h, D1x, D2h, D2x, D70, D100, S1, S2, S3, 14n, 14nx, and SLR/n). It probably also applies to other DSLRs, as well, but since I don't own (many of) them I won't speak to applicability.
It happens to all of us: eventually you'll find an image that, on close inspection, seems to have gotten the freckles (see example, below). No, you don't have bad photosites on your CCD, you have dust on the sensor filter.