hi2all,
how is it possible to imitate scratches like these:
???
i already tried to use a noise texture and mix it with the picture via nodes but it simulates just the noise (oh what a wonder) and not the characteristic scratches …
thx for answering 
Maybe find an old film, and look for blank moments at the start, end, or during transitions, then cut that clip out, find some way of looping it, maybe apply an alpha mask, and overlay it onto your scene?
but is there a possibility to achieve my aim just with the tools in Blender without any filmmaterial and so ?
There is a plug-in inside VSE that does just that. Run your film or a blank thru that, record, and use to feed compositor noodle via image input.
For just a bad developing job, use like a voronoi texture layered on top of a custom texture that is just streaks.
You could create your own scratches pattern with a long and narrow image with dots randomly placed.
Put this image on a plane in Blender and add a camera over the plane at one end. Then add a fast moving to your camera and add some vector blur. this video should be usable in the Video editor to mix with your original shot.
thanks a lot to all of you ^^