If you have a car number, you can look for a photo of a prototype car (or locomotive) to match at a site like RRPictureArchives.net.
Click on the "By Railroad" tab on the left side, then find and click on the railroad in question. There will be two categories, locomotives and rolling stock. Choose one, and list will be ordered numerically. Algoma Central has a relatively small number of entries, so navigation isn't too hard. But for something like UP or other Class 1 carriers, there can be thousands of photos. In that case, use the "Grouped by Range" filter that can be found in the top right corner to reorganize the list into groups of 100 numbers, then select the group that applies.
This is also a handy way to find out if a model offered by a manufacturer is accurate for a given prototype.
Hope that helps,
Jim