Change or remove padlock image with twenty seventeen / UAM

Hi!
I run a WP-site running on twenty-seventeen theme.
The site is set up with user login using the User Access Manager (UAM) plugin.
Problem is that users that are not logged in get a big ugly noaccess-padlock image instead of the teaser images on the front page.

Is there any way to remove or change this image so the not logged in instead get no image or something less ugly?

Thanks in advance!