I just tried out a tutorial by about how to find out if your work might be stolen. [link]. Being just curious, I searched for one of my most viewed works [link] and was shocked. I found my work all over the net, in blogs, on forums, and even on promotion websites... yet, it was even provided to download as a free wallpaper along with several others of my works. Even some authors used them for promoting themselves or their project. Some gave credit at least, others didn't. But all have one in common: None of them asked for permission. Not a single word!
I'm just glad it was one of my personal works and as far as I can see, my commissions weren't affected beside some exceptions. I contacted the provider of the websites or the author of the blog or website where it was possible. But unfortunatelly, some require payed registration or asked for personal data before I can fill out a form or access the contact services. Still, I stayed polite with everyone, asking to put my work down in some cases, asking for credits at some exceptions. But once and for all:

Crediting isn't a greencard for using someones work!
Just because you find something on the internet doesn't mean it's free to use!
If you want to use my work, read my descriptions. If it was a commision or otherwise created for a third person, forget about it right away. Else, ASK!!

Someone once told me, if your work gets stolen, it means it is just really good. Maybe true. But still it saddens me because stealing isn't just using. Stealing is a sign of lack of respect towards the artist. It's not a sign of appreciation at all!