What side is face up when you put photo paper in your printer?

Actually what Cycling-rod said is not completely accurate. It depends on the printer model and how it feeds the paper into the machine. It also depends on what you mean by "top" and "bottom" because the way that it feeds in may not be how it feeds out and, thus, the top as it goes into the printer for the printing process may be the bottom when it completes its journey through the output assembly.

The best way to determine which side of the paper is printed is by looking at the input tray. If it shows an icon that looks like blank page with a corner folded over that has lines in it, then it is indicating that it prints on the bottom side of the paper as positioned in the paper tray. If, instead, the lines are on the main part of the icon and the corner is void of such lines, then it means that the top of the input paper is printed. These marks are usually imprinted into the plastic rather than stamped on with paint so that they will not wear off during use. If you cannot find it, however, mark a page as suggested by Cycling-rod and send a test page to the printer and see where your mark ends up. If it is on the side with the print job, you know that is the side that gets printed.

In general, inkjet printers have a semicircular (or C-curve) paper path which means that the side that is on the bottom in the input tray becomes the top when being ejected and it is on that side that the text is usually printed. The printers are designed to do this to prevent the obvious problem of smearing that could occur if the print side was down upon ejection. Because of this, most inkjet printer drivers reverse the page print order from last to first so that when the job is finished, the pages are in the preferred order for the user's convenience.

Laser printers on the other hand can have a number of paper paths internally. For example, the monochrome laser I have in my office has an S-curve path so that it inverts the paper from the paper tray and prints on what starts out as the bottom side and then inverts it again so that it is ejected with the printed side being back on the bottom. The color laser in my office, however, has a semicircular path just like the common inkjets.

I hope this helps. If you have any other questions, feel free to drop me a line and let me know.