There are a number of different synonyms that could be used to describe "photo-finishes," or extremely close races where it is difficult to determine the winner with the naked eye. Some possible alternatives might include "neck-and-neck," "razor-thin," "dead heat," "nail-biting," "down-to-the-wire," "hairline," or "fine margin." These phrases are all intended to convey a sense of intense competition or uncertainty, as the performance of the competitors is very closely matched and it is difficult to say who will come out on top. Whether you are discussing sports, elections, or any other type of contest, these synonyms can help to add a sense of excitement and drama to your writing.