I'm building a custom FolderThumbnailView (for example I override the Thumbnail paint to draw a semitransparent layer on each Thumbnail in order to visually mark the Thumbnails that are used in my app).

I'm interested to know if/how I can add a small button on each Thumbnail in the FolderThumbnailView on the upper right corner and have an event set to that button.

Thanks

Take a look at this KB:  http://www.atalasoft.com/KB/article.aspx?id=10210

It should give you a good starting point.