philippulus I'd have to think any program that 'gathered' would be downloading them.
If you have 5000 (for example) pics of your own you could rig something offline...
BING is the only option I turn OFF in variety personally (ms tentacles). But you can limit cache if worried about space. It has a few of categories of pic types. Set it to auto start. I know this sounds really shallow but this is one app I can't live without.
Mostly I get NASA's hi-res stuff from chandra, hubble, satellite, mars, time lapse etc. ----Really mind-blowing desktop pics.