There was a bug here, but it doesn't relate to most of the below. I didn't get the checkboxes at all, which is now fixed.
If the checkbox seems to appear in the space above the thumbnail then this is coincidental. It overlays, on hover. The height is coded into the CSS and if it's too much some CSS changes would be required (the image is centred vertically).
Only those with delete permission will get the checkbox.
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#2816 - Missing select option on most recent entry and request for title in overlay
If the checkbox seems to appear in the space above the thumbnail then this is coincidental. It overlays, on hover. The height is coded into the CSS and if it's too much some CSS changes would be required (the image is centred vertically).
Only those with delete permission will get the checkbox.