on a related note, hosting images on your server for users on other servers, eats up a lot of resources too. I know some instances have stopped allowing saving of images.
I suppose if you wanted to be really certain your uploaded images would remain under your control, you could post them to a PixelFed instance and point it to your own domain like images.mydomain.com. That way you could always redirect them if your PixelFed instance goes down.