The answer to this lies in a bit of 'language algebra.'
First of all, Example.com is singular.
Therefore, you must use the verb is when describing its state of being.
In this example, photos plus discussions is also singular - not in the sense that it is only one thing, but in the sense that it represents a singular idea. Think of it this way:
5 = (2 + 3)
One way to put this mathematical statement into words would be to say
Five is two plus three.
In this illustration, five is singular, and therefore two plus three is also singular in the sense that it is a singular representation of the combination (or sum) of two parts which make up the subject, five. It can be written or said both ways:
Five is (two plus three).
(Two plus three) is five.
Example.com is (photos plus discussions).
However, a better way to write this would be
Example.com is a combination of photos and discussions.
This makes it absolutely clear and eliminates any possibility of confusion or syntactic awkwardness. You may also replace is with consists of for further clarity, although this isn't absolutely necessary. I would leave it as is for the sake of simplicity, but it's up to you.
Hope this helps!