Earth Cloud Opticaлббьюбюююббббббдддждюб l Thickness, April 2001.
False-color image shows a one-month composite of cloud optical thickness measured by MODIS and averaged globally for April 2001.
Optical thickness is a measure of how much solar radiation is not allowed to travel through a column of atmosphere.
The NASA website hosts a large number of images from the Soviet/Russian space agency, and other non-American space agencies. These are not necessarily in the public domain.
The SOHO (ESA & NASA) joint project implies that all materials created by its probe are copyrighted and require permission for commercial non-educational use. [2]