Hi

this link can be useful

http://freegisdata.rtwilson.com/

What do you mean by Geographic image? are you referring to satellite images or something else. if you are talking about publicly available satellite images and other satellite based preprocessed datasets, these links may be useful. 

http://earthexplorer.usgs.gov/

http://glovis.usgs.gov/

You can also get access in google earth engine,

https://earthengine.google.org/#intro

which is free but not publicly available at this point you have to ask permission to get access in it.

maybe this one http://rapidfire.sci.gsfc.nasa.gov/gallery/