The Oxford Living Dictionaries says the following, about the usage of or. (Similar definition was given from the NOAD I had installed on my Mac Mini, the copy that comes with the Dictionary application together the OS.)

Where a verb follows a list separated by or, the traditional rule is that the verb should be singular, as long as the things in the list are individually singular, as in a sandwich or other snack is included in the price (rather than a sandwich or other snack are included in the price). The argument is that each of the elements agrees separately with the verb. The opposite rule applies when the elements are joined by and—here the verb should be plural: a sandwich and a cup of coffee are included in the price. These traditional rules are observed in good English writing style but are often disregarded in speech.

In a sentence like one or more photos are better you use are because the noun closer to the verb is plural (more photos).