The red and orange legs are one picture. Mirrored and flipped to form a border. It’s basically a picture I took, and then used the color toning in RT to give them the weird skeleton look.
The inner circle started with this picture:
I isolated the legs to turn the black background transparent. Then in GIMP, used the GMIC droste filter to make the repeating leg spiral. I basically screwed with the droste filter settings, made a dozen different versions and saved them to disk. Checked them every morning when I woke up and deleted my least favorites until I got down to one picture, which was used as the center of the finished piece.
I used G’MIC “Inpaint Transport Diffuse” filter to smooth over some sharp edges near the center of the droste effect.
Warp transform towards the edge of the circle to paper over some oddities in the looks of the droste.
I masked the legs with a circular selection, and drew in some little fingers on the mask, then gaussian blurred the whole mask to make is so there is no really definitive beginning or end between the middle part and the outer part.
Finally I did a gradient map on the middle droste legs to complement the color of outer orange/yellow legs.
The outer orange/yellow legs were done only in RT. The inner part was a little bit of RawTherapee, and then a lot of GIMP and G’MIC.
I hope you like.