You are correct that there is nothing on the photo itself that tells you the source of the photo itself, and it only says that you are the submitter. (I agree that is weird and MyHeritage should change that).
But what you can do is go to the person for whom that photo was added. You should find at the bottom right of the person's profile page that MyHeritage automatically entered a source citation as to how the person was automatically added, e.g.:
Then you can click on the link beside "Source:", which in my example is: "Smart Match™: Rudy Web Site", and it will bring up a page showing all the information that was brought in, and a link to the web site.
Go to the website it came from and find the person with the picture you're looking for. Don't bother looking at the picture because it won't tell you anything (again, MyHeritage should allow sources on pictures). But once again go to the Source citations at the botton right of the person's profile page.
Now what you see is the source of where the person who you got this from got it. Click on the link beside "Source:", which in this case is "FamilySearch Family Tree" and if the person has given you permission, you can see their source. Otherwise, you at least have the person you got the picture/information from and can contact them for more info and to work together.