How does Google Imaging & satellite spying photo analysis work?

I'm a layman, so, keeping it at lay-talk, fundamentally, how does Google Images recognize two images as having the same provenance?
And, is it similar to how software find tanks and missiles in a spy satellite photo?
What I have been told is that they both do an FFT on the pixel information, and, from that detailed frequency data, they look for characteristic "signature patterns".
But, I know no more than that (and even that may be wrong).
Can you shed light (in layman's terms) on this process?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 05/19/2014 12:55 PM, Liam O'Connor wrote:

Lots of DSP, trial and error involved in calibration and proofing. Mostly automated, ground penetrating radar, bizarre optical wavelengths, magnetometers, etc. all integrated in proprietary computer systems. Between the oil companies and the spooks, remote sensing is very mature and still very secret. FFT analysis can make anything more visible, to a point.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.