I assume you are refering to the photos that we are told Paul had painstakingly collected in his scrapbook as part of his plan to escape to New York at some point in his life so that he is able to flee his monotonous middle-class existence and life the upper-class life he has dreamed of having for so long. Note what the text tells us about these photos:
Not once, but a hundred times, Paul had planned this entry into New York. He had gone over every detail of it with Charley Edwards, and in his scrapbook at home there were pages of description about New York hotels, cut from the Sunday papers.
Clearly, this descriptive detail shows us that Paul has considered this flight in great detail, and the way that he has collected photos and information about hotels in New York shows that he has done a great deal of research so that he is able to play the part of the rich young man and not seem out of place. The impact of this detail is to heighten the sense of Paul's desperation and the extent of his fantasy. He is so unhappy living his own life that he obsesses over the kind of life that he could live if he were rich. The extent to which his dream life is built on illusion and fantasy never enters his mind.