Q: Batch process images I have to transform a few hundred images every day in a specific way.
I need the best freeware tool or a piece of C# code that supports batch watermarking, resizing of images and can be automated (old configuration can be reused).
What tool do you suggest?

A: Dave Winer of scripting.com fame has been posting about his success with ImageMagick. I think its free. 

A: IrfanView has pretty decent batch image processing/conversion support.

A: If you want to roll your own solution (and I'm guessing that's why you tagged the question with "C#") the GDI+ stuff built into the framework (System.Drawing and its children) are pretty powerful, more than enough to accomplish what you'd need.  The advantage of this approach is that you can define your own transforms and apply them en-mass, should you choose to code it that way.

A: Look at the Netpbm collection.  It contains over 300 tools and supports hundreds of graphics formats.  You can easily experiment with the process you want to accomplish using the tools one by one, and later bind them together into a script.  This is open source code, so if you want to obtain the maximum performance, you can even package together the code that interests you ina stand-alone program.
You typically work with netpbm by combining tools into a pipeline.  So, you would use pamscale to scale your image, and pamcomp to combine the result with the watermark.  If the watermark varies with each image, you can use pbmtext to create it.  

A: There are a lot of examples out there of doing these sorts of image manipulations with C#, it isn't very difficult.
Here are two articles from Joel Neubeck which resize and watermark an image. 
http://www.codeproject.com/KB/GDI-plus/imageresize.aspx
http://www.codeproject.com/KB/GDI-plus/watermark.aspx
You could package these up all together and write a simple program to process all the images while applying these operations. 

A: See the IMG Convert at http://www.abadev.com
