Hi Rashi, 

If you would like a different image for each knowledge base, it is a little more complicated.

If you have relatively few knowledge bases, your best bet is to create additional EVAM configurations and templates for each knowledge base, using the conditional filter within the configuration, and referring to a different image in each of the new templates. 

The other approach, that I would only use if it was absolutely necessary, is to change the image via a search script post processor. The scripting interface is well documented and you want to keep processing in these scripts to a minimum.