Well, I found a solution that fit my needs. It may help others, too.
1. use any (I suppose) photo manipulating software on hand
2. open the original Kubik header in this program and cut the content out, so the “frame” remains.
3. open the picture you wish, and fit it in the remaining “frame” (not in technical terms).
4. Save the new image – the Kubick “frame” and your picture – and name it “personalheader.jpg”.
5. Store it on your database.
It helped me to solve the problem quickly. It seems not to be the “state-of-the-art-solution”, as if you change the background colour from grey to else, the “frame” will remain grey, as it is part of the picture.
Should anybody find the “high tech solution”, I am glad hearing from you.
haveanicewik
Andrew001