To 
alter  your index settings, open the 'start' menu and type 'index' in the 
search bar. Hit ENTER.

When the 'indexing options' window appears, click the 'advanced' button, then 
choose the 'file types' tab.

   Sadly there is no 
'uncheck all' option here. Most of  the file types here you 
will  never use, so feel free to uncheck them and remove them 
from the index. 
If you use the desktop search to look through many photos or documents, 
consider dropping all extensions except '.jpg' for photos and '.doc' and '.xls' 
for Microsoft office documents. Your needs may vary of course. When you have 
finished your selections, hit 'ok' and the index will rebuild itself.