I use an Epson Expression XP-750 with Windows XP so my Printer Preference box layout may not be exactly the same as yours, but I hope I can offer some advice.
Have you opened the Printer Preferences and selected the Rear Paper Feed Slot from the paper options on the Main Tab? If not you need to do so otherwise the printer won't use the Rear Paper Feed Slot.
If you have selected the Rear Paper Feed Slot you must wait until the screen on the printer tells you to load the paper before you insert it into the Rear Paper Feed Slot. If you load it too early it will just feed straight through the printer without printing your picture.
You can select A4 Photo - Portrait or A4 Photo - Landscape on the Shortcuts Tab to make the settings selections easier, but you will still need to set the Rear Paper Feed Slot as the paper source.
If you do get your printer to print okay from the Rear Paper Feed Slot you might want to add an extra printer driver for the XP-750 set up just for printing photographs via the Rear Paper Feed Slot. You can do this with the Add a Printer option, but just make sure you give it a different name from your present printer driver name otherwise you may overwrite the original one.