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Until MacOS 10.7, I used to put a png file in a read/write dmg, then I set it as its background picture, then I hided it and converted the dmg to a read-only one. Everything just worked.

Now, in MacOS 10.8, if I do the exact same thing, when I open the read-only dmg it opens the read/write one too. It looks like it "knows" the original background picture is on the read/write dmg. Even if the read-only one has the same image in its contents.

How can this be prevented?

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are you certain that the background picture on the read-only disk image isn't an alias of the one on the read/write disk image? –  Ethan Lee Sep 8 '12 at 22:11
    
I create the rw dmg, then I convert it to a ro one so its contents are the same –  user732274 Sep 8 '12 at 22:30

2 Answers 2

You're right. The original disk image is opened when opening a newly converted read-only image. However, I found that if you delete the original read-write disk image, Finder (actually, DiskImageMounter) has no problem mounting the read-only image without its original. DiskImageMounter itself is not really responsible for the behavior you are talking about; if you look at your read-only image's .DS_Store file in TextEdit, you'll see (amidst very obscure symbols) your original image's name and file path in many places. This is just built-in behavior of Mountain Lion, I suppose. Unfortunately, there are no workarounds except for deleting the original image (and emptying the Trash) because Disk Utility is ultimately responsible for the creation of the DS_Store file, and the image created is read-only.

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The problem is that I need to keep the rw image too... Very odd and very annoying... –  user732274 Sep 9 '12 at 10:35
    
@egon1984 You don't have to delete the rw image. At least when Finder does mount the ro image, the rw image is only mounted and not opened with its own window. As long as you're not concerned with memory usage due to mounting the image, you should be fine –  Ethan Lee Sep 9 '12 at 22:41
    
Ok, that's right... but I still have to select two drives before unmounting them... still a bit annoying. Anyway, I'd like to know why the rw image gets open... –  user732274 Sep 9 '12 at 22:46
    
@egon1984 As I said in my answer, some of it has to do with the .DS_Store file. If you take a look at the ro's .DS_Store file, the original image's file path is strewn all over it among obscure symbols –  Ethan Lee Sep 10 '12 at 3:54
up vote 0 down vote accepted

So, I FINALLY figured it out... Instead of deleting the rw disk image, it is enough to rename it.

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