OK, take a deep breath. We are going to venture, ever so quickly, into Terminal.app. The problem should be easy to fix. If the files have the read-only attribute set, we just need to reset it.
So, fire up Terminal.app, and navigate to the folder where all your JPGs are. Navigation is easy: type:
For example, if you dragged all your JPGs to your Pictures folder, you would type:
Now that you are in the folder of interest, type the following incantation into Terminal.app:
This command is the "change mode" command. It modifies file permissions. The "ugo" part standard for "user, group, others", which means you are going to change the file permissions for the file's owner ("user"), the user group that owner belongs to ("group") and everyone else ("others"). The "+w" part sets "write permission" to the file (the lack of write permission to a file is the Mac OS equivalent of Windows Read Only bit. The "*.jpg" selects all of the files with extension ".jpg" as the target of the preceeding command.
So, that one command will set write permission to all of your jpgs, allowing you to manipulate them to your heart's content.