In most cases it's,
A. Just a link which happens to be a jpg. Which means it the website wants to change the jpg they can or if the website goes down it points nowhere.
Or B. Just a hash, which might supposed to be a unique representation of a specific image, but really is just a string of characters, so different sites might disagree what that image is.
If you're talking about an IPFS hash, That's a hash based on the image's content on a very specific network. The same image content will always hash to the same key.
Oh it's even stupider than that.
In most cases it's, A. Just a link which happens to be a jpg. Which means it the website wants to change the jpg they can or if the website goes down it points nowhere.
Or B. Just a hash, which might supposed to be a unique representation of a specific image, but really is just a string of characters, so different sites might disagree what that image is.
If you're talking about an IPFS hash, That's a hash based on the image's content on a very specific network. The same image content will always hash to the same key.