Thank you for the reply.

As far as I know, everything is fine, but it's still not working for me.

When I disable caching, which includes pngs, and then use 'location ~* ^/card', I am able to access the images normally without capital letters, but still not with capitals.

With caching enabled, I cannot access images at all with the 'location ~* ^/card' setup.

Caching is the main reason for me needing '^~' on my location block, so that I can disable caching for these images alone.