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I have created a .dmg of my Pictures library via Disk Utility in Recovery Mode as an emergency back up last night, before erasing my Macintosh HD. I did the same this for Documents and iTunes, all in separate .dmg files. Documents and iTunes mounted and opened just fine, and I recovered everything, but the Pictures .dmg gives me the "Corrupt Image" error when I try to open it:

.dmg error message screenshot

I have tried using Disk Utility (no luck with mounting, verifying, converting or adding Checksum, all gives me the corrupted error)

I have tried:

  • extracting DMG using 7Zip – not working
  • converting it to another format like ISO – not converting
  • opening DMG using Disk Drill – not opening
  • opening DMG using Data Rescue – not opening
  • the hdiutil and related commands through Terminal – nope

I have tried third-party apps, and it seems like they don't even 'see' the .dmg file due to its corruption.

Hope anyone can help or clarify if it's broken forever so I can stop trying to open it.

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Occasionally, if the gatekeeper (system preferences/security & privacy) does not recognise a .dmg file as being from a developer it gatekeeper refus to allow it to be mounted.

It usually states that the file is corrupt or something like that. This normally only only applied to .dmg files with applications. However it may be that it is getting confused with your file.

There is a hidden menu that you can activate to allow the "anywhere" option. This will get around this "feature".

Here is some info about it. http://osxdaily.com/2016/09/27/allow-apps-from-anywhere-macos-gatekeeper/

If you are able to mount your .dmg image and copy your files off reinstate the normal gatekeeper menu, as it is a good security measure.

If this does not work and your .dmg file is uncompressed then you may try a program called file juicer. https://www.echoone.com/filejuicer/

This application will interrogate files, .dmgs, applications etc. and extract many types of files from them (including many image formats). It may not work with compressed and or encrypted .dmg files.

If it is not registered it will place a watermark in any images it extracts.

If you accidentally encrypted the .dmg file you will need to use the password to open the it.

It is always good to have a couple of backups of your files/system.

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