I'm trying to reduce the size of my iPhoto library. I copied and burn the library of photos onto a DVD. When I go to open a picture from the DVD I'm prompted "the picture is used by Mac OSX and cannot be opened" What's up?
How did you burn the DVD? Through iPhoto or through Toast or something else? Sometimes when you burn a data disk the file format changes (you can tell if the icon is unusual). You might have to drag and drop the file to your image viewer, or possibly copy the data back to the hardrive and change the file format back to .jpg or whatever.
Process
I opened iPhoto which showed all the pictures in the library. Went to file - select all - copy. Inserted the DVD and doubled clicked on the icon. Then right clicked on the DVD window and clicked paste items. After that clicked burn.