This blog post was inspired by an issue which recently occurred in my own workplace.
Several months ago, while reading an employee-only internal newsletter published by my employer, I happened to recognise a photo (shown below) that had been used in the headline of the newsletter, and was also used on the company intranet (linking to the newsletter).
That particular photo is available on my website, and is clearly labelled as a copyright image that cannot be used without permission. No-one had requested my permission to use the photo.

Canon EOS 350D, 17-85mm IS @76mm, 1/125 sec, f/5.6, ISO400
Some digging through my webserver logs indicated that a colleague had found the image while doing a Google image search for images relating to autumn.
I only happened to see the photo in the publication because I'm an employee of the company, and hence have access to this particular newsletter. If the photo had been used in any other company, I wouldn't have noticed!
If you notice that a colleague has "stolen" one of your photos, and is using it without your permission in an internal employee-only publication, what would you do?
Post details on how you would respond using the comments facility below.
I'll be posting details in a future blog post on how this particular issue was handled.
Edit: I've posted a follow-up article here.
I was just reading about a copyright infringement (http://www.photosig.com/go/forums/read?id=238502) and then came along your post.
It's an un-fourtunate situation and I'd find it a difficult one to deal with. How many people are in circulation and seeing the photo? Perhaps ask for credit/reference whenever it's used? Personally I would probably avoid chasing money for the usage as afterall it's your work force and could create an ugly situation?