When you copy to a CD-R, the R means "write only".
So, you can copy (write) files to a CD-R and you can read the files after
you copy them on the CD-R but you cannot edit the files on a CD-R. This is
why you are getting the message "READ ONLY CD". Also, if you want to delete
a file from a CD-R you will get a message that you cannot do so. Any file
copied to a CD-R is permanent. You can add more files to a CD-R ( up to
about 600 MB to be safe not to exceed the 700 MB capacity of a CD-R) but you
cannot delete any file from it and you cannot edit any file on it. So in
essence you use a CD-R to copy your photos and you keep them there as a
backup copy of the photos on your hard drive or to send and distribute your
photos to friends.
Now for your problem. Easy to solve. If the photo is on your hard drive, you
open it and edit it and "Save as" and give it a different file name. After
editing the original file you can copy the new edited file to your CD-R (you
simply insert your CD-R instead of a blank CD and follow the same procedure
you used to copy to your blank CD).
If after copying the photo files to your CD-R you deleted them from your
hard drive, there is no problem. Select the file you want to edit on your
CD-R and look at the menu on the left of the file names. Click on Copy. A
window will open for you to select a folder you want to copy this file to on
your hard drive. Select a folder and the file will be copied back to your
hard drive. Then open the file from there and do the editing.
The "R" in CD-R does not mean "write only." That's absurd. It means