Even though I have created the field Photo1 of the image type in the Rental Unit Database Collection, I am not able to retrieve the field value in the Rental Unit Details screen.
Unfortunately, I cannot share the screenshots uploaded on a public server here I took describing what my attempts were but if you look at the attached file, it should give you a pretty good idea.
(The field name in the database collection is actually called Photo1, I tried to add it in both screens although I think it should only be added in the Rental Unit List screen available data)
On your 1st screenshot with “Rental Unit Details” screen selected, you can clearly see that there is “No Linked Data” to this screen.
This is the only reason why you can’t access the image (and other details about rental unit).
So, it seems that you’ve set up the connection from “Rental Units List” to “Rental Unit Details” screen incorrectly.
I guess that on Rental Units List screen you use a simple list. Did you set up the connection there? Or in some other place?
Add an action to this list to Link to the details screen, remove previous connection and all should work fine.