The Image Gallery is provided as a complimentary
source of high quality digital photographs available from the Agricultural
Research Service Information Staff.
Oldie but a decent one from the government for images and pictures. Remember that with most government sites you are free to use the pictures but some such as NASA do require that you cite the source.
The internationally recognized WorldImages database provides access to the California State University IMAGE Project. It contains almost 75,000 images, is global in coverage and includes all areas of visual imagery. WorldImages is accessible anywhere and its images may be freely used for non-profit educational purposes. The images can be located using many search techniques, and for convenience they are organized into over 800 portfolios which are then organized into subject groupings. To explore them click below.
via Jackie Gerstein