For images added via the Upload option on the Image card, the main workaround I can think of which doesn't involve a hosted image link is providing guidance to users to right-click the image and choose "Open image in new tab" (in Chrome, or the equivalent in other browsers).
Depending on the reason for needing the image to be opened in a new tab and the broader use case, you could also explore creating/embedding a simple Experience Builder app to wrap the images and embed that in the site.
-Rylee