You will all have noticed that there is a clear trend in English to give particular emphasis to the most important items of information in any utterance. English speakers tend to "package" their spoken production in such a way as to highlight what they consider to be the essential elements of the message they wish to put across. In this particular case, it is most likely that the speaker will highlight the words "photographer", "corner" and "street". As a consequence, he (or she[2]) will tend to reduce the stress he gives to the other, less important items in the sentence. To illustrate what I mean, by taking this to an absurd extreme, an utterance such as "hum hum hum photographer hum hum corner hum hum street" would probably be understood. In a particularly noisy situation, people might not even realize that what you had actually said in place of the unstressed syllables was "hum hum" etc. and would assume that they had not been able to identify the sounds clearly because of the high level of background noise. They would I believe almost unconsciously substitute the predictable words "There was a", "at the" and "of the" in place of your hum-humming.
On the other hand an excessively full pronunciation "There was a photographer at the corner of the street" would be ridiculous, unless perhaps the sentence was pronounced under specific a-typical circumstances, as for example during a dictation exercise. There is no point in ordinary life wasting people's time by stressing predictable, relatively uninformative, and therefore largely redundant parts of sentences. Hence the need to stress the informative parts of an utterance and not the rest.