i work for a company that provide product images to retailers.

i've been asked to look into watermarking images and how we would discover if someone had reused an image without their consent.

i've looked into several ways of using visible and invisible watermarking on images and i've written some v basic apps that do both, but now i need to think about how to discover web site that are using the images without consent.

i figure it would be good if i could write a webcrawler in c# that i could point against a specific web site (www.boots.com for example)
and which would then crawl thru the site and save any images to a folder on my pc. i could then use my watermarking program to analyze the image for my watermark.

i've seen a couple of seemingly complex examples of webcrawlers, but what i'm after is an explanation of the basics. (i am rather dense) for example i unsure how i would get images from a web site and put them in my local folder. can i do that within a httprequest?

if anyone can either explain the basics or point me towards a good basic tutorial i would be very grateful.