Use a script with Insert from URL or GetLayoutObjectAttribute to lode a text field with the contents. Then search for all records where that text field is empty.
The source pages I want to look at contain only a photo.
Usually, there is at least some tags to control how that photo is displayed. Have you checked to see what you get if you try this?
Also, see if Insert From URL can insert that photo into a field of type container. I believe that it can and then you can search for empty container fields.
I couldn't find any code. I was wondering before: how do you search a container field if you can't enter any text into it?
Set up a calculation field:
IsEmpty ( container field )
Clear the do not evaluate if all referenced fields are empty check box.
Search for a 1 (True) in this calculation field.