The Viking Orbiter Visual Image
Subsystem (VIS) Experiment Data Record (EDR) Image
Archive is a complete and fully-documented archive of
images of Mars collected by the two Viking Orbiters
(1976-1982). A total of 50,500 VIS-EDR images are
archived on 46 CD-ROMs. The documentation includes event
information (the reasons why certain image sequences
were planned) and a list of "lost" images with an
explanation of why they could not be recovered.
This data set is online here and at
the PDS Imaging Node. The Imaging Node offers a search
capability for this data set using the Planetary Atlas.