I have been working with Atalasoft for our C# / WPF image viewer. I needed to get mouse actions on the annotations so I could show a pop-up menu when you right clicked allowing you to delete the annotation or edit its properties. Their current release had no support for what I consider a common need.
I opened a case file with them in and less than a week they got back to me with a hotfix I pulled from their FTP site with support for MouseUp and MouseDown actions. Works like a champ. They have been very responsive with all requests I have sent their way. Our software / legal folks are working with them to get the proper licenses so we can use their DotImage product in production.
So far I consider them Highly Recommended if you need to support a lot of image formats in .NET