You cannot delete a Image URL from the Web UI

[jleach]

If you mistakingly enter a URL in the Image URL field it cannot be removed after. Saving results in an error once the field is cleared.

[loneil]

This might still be an ACA-Py bug where having a blank value for image url breaks connection creation, and the endpoint does not allow nulling out the field, only blanking it if it's been previously entered...
I'd forgotten about this but will check it over again since there's been ACA-Py updates