I have a few hundred photos of manhole covers (and other markers set in the ground, like survey markers). My "collection" started in Tampa and at Disney World. Friends and relatives send photos when they travel, particularly abroad. Disney parks have their own themed covers for their newer "lands" and some hotels (like Port Orleans, Galaxy's Edge and Pandora).

Photo tips:
try to have the camera directly over the cover so you have a perfect circle rather than an oval
Position yourself so your shadow doesn't intrude. After all, you can always take a picture sideways and then straighten it for viewing
Try not to cut off any part of the cover; include enough of the pavement around it so it can be straightened if necessary without cutting off any part of the design.