ScreenCloud is a screenshot utility with releases on every desktop platform, which also has a plugin system.
I created a plugin for it that supports the Caddy upload extension to automatically upload a screenshot to your Caddy-powered server (with some extra options), as well as supporting HMAC-SHA256.
While making this I ended up making a python module for the upload extension should anyone need it: GitHub - p3lim/pycaddy: Python module for using Caddy's upload extension
Just another neat thing for your selfhosted world.