How do I put my photos back onto my cameras SD card?

Dammit. I did misread the q when responding with this:
Your card reader loads just like a drive on your computer.
If you are on a pc you will have to cut and paste toad to it.
Apple just drag and drop.

Hook up your camera and look to see if it shows up as an external drive on your computer. If it does you can follow the steps above.

^This is exactly what I was gonna say. :)

Except you’re going to add to the card, not toad it. ;)

Is your camera a Canon by chance? They and a few others don’t follow the USB Mass Storage protocol so the drive will not show up in the Finder. The easiest way is to get a card reader. They are cheap.

Plug the camera in and fire up the Terminal and enter:
ls -al /Volumes

Let me know what the output is.

Edit :: And on some cameras you need to turn on Mass Storage in the menu on the camera. Sometimes it is called PTP too.. I might be wrong about the last one, but it is something like that.

Does your printer have a card slot? If so you can use that as a normal card reader.

#1 – Most cameras, when connected to the laptop, show up as an additional drive (similar to USB pen drives). They allow copying of files both ways—ie, you can also copy files from your laptop on to the SD card. Did you try this? (You may have to use the regular file browser of your laptop and not the photo management software that came with your camera)

#2—Many laptops do come with a SD card slot these days. If your laptop does not have but you know a friend whose does, you can simply carry your photos on a USB drive to that laptop and copy them to the SD Card—using his laptop, plug in both the USB drive with the photos and the empty SD card into his laptop and copy files from the former to the latter.

Hope this helps.

Card readers are so inexpensive! Just buy one!