Smart pics

I have this problem: I write presentations and sometimes I need a great picture to tie it all together. You know like when you want to say that what you will see is going to blow your mind and you put in a picture of a street sign that ha s been painted over and now says "Go ahead! Danger awaits!"...so everytime I ask myself where to get these smart pics from. Getty does nothing for me and google pics is simply prey to the users' own inability to tag pics right.

So can someone point me to a good source of interesting pics (please please do NOT say flickr), pics that have inherent interesting messages, pics that are great conversation bonding agents?
Or does someone what to help me make a data basis of these? This one I have from signspotting.com and there's also some cool ones in this presentation from Interesting 2007