Unfortunately, with digital cameras (and phones) in the hands of the the masses, there can be a presumed "lesser" value on photography. It's the same mentality that prompts someone to think, "Why should I hire you when my nephew just got a perfectly swell camera for Christmas".  Some folks simply feel that if an image is "right there" on the internet, then justified ownership and usage is just a "right click" away. Once in awhile I find my images on sites and request that they be removed, but then again, who has time to be on constant patrol? 

I recall a situation back in the day when illustration work was ripe. A well known Illustrator had used a well known Photographer's photo as reference for a project, but for reasons unknown, copied the image to a "T". It was a big campaign and the Photographer immediately recognized his work, resulting in the Illustrator and his agency client having to pay a hefty sum.

Times have changed, no doubt.