vivalasvegas - 6:41 pm on Oct 24, 2012 (gmt 0)
Thank you. In the meantime I found Adobe Illustrator's 9 Slice Scaling which seems to be a tool built for this task (scaling portions of images). Unfortunately it doesn't work for some reason. It might have sth to do with the fact that my image is a GIF. I'm not a designer and these Adobe tools are all new to me.
I will try to use Photoshop.