Please do not laugh, it is truly hard. Trying to come up with one strict rule about definiteness in English (I wasn't able to find one) I collected some information and ask to check it out. Does that work?
We use THE when there is only one possible variant OR the noun following a definite article is well known to both ourselves and the listener.
I want to show you the photo of Jane and me. would be appropriate either when the listener is familiar with the photo OR there is only one. Even if the listener doesn't know what photo you're talking about, the uniqueness of that photo forces us to take THE.
After hearing that, the listener unable to identify the photo decides that there is no more than one, therefore, there is no apparent reason to ask which one. He either identified it OR it is unique.
We MAY have to add a qualifying clause with OF (or another preposition), but that's not necessary.
Uncle Vernon sat back down, breathing like a winded rhinoceros and watching Harry closely out of THE corners OF his small, sharp eyes.
In this example, THE relates to OF. All that goes after OF just makes clear what corners we mean and so creates uniqueness. It wouldn't be coherent to ask 'Which corners of his small, sharp eyes?'
Concluding, it is not a must to take THE in sentences with a clarifying clause (like Cars are a major source of pollution in cities.), but sometimes the two parts are closely related. (like The life of a polar explorer.) Another example of that would be
Of THE 2 testing programs I USE the 860 Pro has outscored everything else I've ever tested.
Does that make sense?
I'll be glad to hear If someone has some suggestions to read about the topic.