It should definitely be off--and probably under the control of the course designer as to whether a student could even use an overlay. I use my own photography for the dashboard cards, and I find it irritating when I notice that students are seeing a shoddy, worse version of the course I designed. And, I am auditing an art class, where the card image is a famous photo. It's really tampering with core content to have an overlay.
But I would settle for "off by default" and probably will never get my wish that I can prevent use of an overlay.
But, hey, I'd prefer that Canvas show students their assignments and grades in the categories I created rather than the messy and confusing date. I realize they can toggle to categories, but many don't realize that, and I don't really think the date order helps my students in the least. But that is another issue.
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