Are users allowed to copy the referenced egg-shell.png and host it themselves or is this connected to some sort of metric you like to gather?

If you got to the site hosting the image it says:

/* This is mostly intended for prototyping; please download the pattern and re-host for production environments. Thank you! */

Yes, thank you for answering. The textures are free to use, but the URL should only be used for prototyping. Here is the website: https://www.transparenttextures.com/