I can't stand imgur. You can't upload photos without an account, and the adds are as obnoxious nails on a chalkboard.
You can upload images without an account, but Imgur won't allow you to resize them or perform other changes that are available only to registered users. You can also not delete an image you uploaded if you aren't registered. I don't see any ads, but I am using ad-blockers. The site is ad-free on my end.
However, with VPN that I use sometimes, it does not allow to upload image.
I have noticed that as well. That's a new thing. Up until a few months ago, they didn't mind VPN usage. But it probably also depends on the type of VPN. The more exclusive and expensive ones might work, while free VPN software could be blocked because of misuse.