when i have a sequence of individual pictures, how can I create a single frame like this? My tools are GIMP and/or Darktable. Kindly help.
You're looking to create a Composite image. The basic workflow for this is as follows:
- Combine all images into one file as layers
- Align the layers
- Sort layers
- Mask the layers
Here is a tutorial from SLR Lounge on how to do it with a sports shot. The same techniques and methodology apply to GIMP. To align the photos I would recommend using Microsoft's Image Composite Editor. With it you can align the images and export them as a single .PSD file which GIMP can open. You can also align the layers by hand.
Edit: Your post is tagged as astrophotography. Are you looking for a program like Deep Sky Stacker?
As a whole you aren't clear about what you are looking to do.
If you want to make someting similar to the image you linked to, Hairy Dresden's method is the way to go.
If you want to stack a series of images in which one item is moving, you could try using 'align_image_stack' or Hugin (align_image_stack is part of the Hugin package) to align the images. You'll probably have to remove or add control points by hand.
Using masks, you can also blend the different images within Hugin, and then use GIMP to finish editing the composite.