Before World War II, most corporation annual reports were dry recitations of data, often using the same wording from year to year with only the numbers changing. After the war, new printing techniques combined with a desire to improve public relations led most companies to prepare more visually appealing reports, with color photos on the cover and color or black-and-white photos inside. This oversized–9″x11″–Union Pacific report is an example.
My collection includes just a few annual reports. However, another source of annual reports is the Hathi Trust. This institution has most, if not all, annual reports from 1922 and before for the Union Pacific, Great Northern, and several other railroads. Unfortunately, unless you are associated with an institution that is a partner of the Hathi Trust, you can only download the reports one page at a time, which can be tedious.