As of yesterday, all images on the site have reverted to a strange unknown image. All original product images are not appearing.
Has anyone else had this issue? I've tried contacting support, but it seems as though it's next to impossible to get a hold of them.
Looks like someone got access to your store and is trolling... update your password
I checked out your site and didn't see that image, so assuming you fixed it already.
Another key thing to check: see who has access to your store (staff + collaborators) and remove anyone that isn't necessary, and only give permissions to people as they need them.
Shopify support can also check their logs to see who (what user / app) changed the images. It looks like a security breach so I would let them know that in your support request. Their support is slow but they usually get back eventually for something as serious as a security breach.