Hi!

Take a look at the displacement map filter
https://docs.gimp.org/en/gimp-filter-displace.html

This can accomplish the effect you are looking for, but the hard part is coming up with an appropriate displacement map to use. Simple effects like a rippling flag can use a simple sinusoidal grayscale gradient as a displacement map, whereas things like crumpled paper are best served with 2d noise displacement maps.

I find that in addition to the actual displacement distortion, placing the actual displacement map in a layer above with an overlay or hard light blend mode can add in the shadows or highlights to really sell the look.

-Rob A>

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