.jpg can’t be opened because it is from an unidentified developer.

macOS Sierra: Open an app from an unidentified developer

Text below is from the above link.

If you try to open an app that is not registered with Apple by an identified developer you get a warning dialog. This doesn’t necessarily mean that something’s wrong with the app. For example, some apps were written before developer ID registration began. However, the app has not been reviewed, and macOS can’t check whether the app has been modified or broken since it was released.

A common way to distribute malware is to take an innocent app and insert harmful code into it, and then redistribute the infected app.

The safest approach is to look for a later version of the app from the Mac App Store or look for an alternative app.

To override your security settings and open the app anyway:

1. In the Finder, locate the app you want to open.Don’t use Launchpad to do this. Launchpad doesn’t allow you to access the shortcut menu.
2. Control-click the app icon, then choose Open from the shortcut menu.
3. Click Open.The app is saved as an exception to your security settings, and you can open it in the future by double-clicking it just as you can any registered app.

Note: You can also grant an exception for a blocked app by clicking the “Open Anyway” button in the General pane of Security & Privacy preferences. This button is available for about an hour after you try to open the app.

To open this pane, choose Apple menu > System Preferences, click Security & Privacy, then click General.

Since these are not apps, this error message makes no sense, especially since they open with Preview. How did you transfer your images to the new Mac? Did you give yourself the same user name on the new system? Does PS 6 launch and run normally? Are you trying to open the images in Photoshop by double-clicking them in the Finder? If yes, what happens when you open them from within Photoshop?

I am having a similar enough issue. Has there been any progress made?

I'm an artist and browse images for inspiration and practice. I will drag and drop many to come back to. Until recently it was fine, and the image files would open for me to flip through. Now, dragging leaves a file image "from an Unidentified developer," whatever that is. I never had the issue before. It's the same old computer, mouse, everything I've had for awhile, so I can't blame it on new equipment, but maybe it was in the update I ran. I don't remember.

Per other comments, I've looked at Security/Privacy-general...and I dont have this "anywhere" option that is mentioned.

Restarted the computer, restarted the finder, deleted the plist files one troubleshooting post said to (and restarted after)

Thanks

Do we get an email or something when a reply is made to this thread?

Make sure your macOS and Adobe tools are all patched to current. If theykre not, apply the patches and the updates.

If the problem persists and with the image (re)located in your login directory and with the image here assumed to be named image.jpg, launch Terminal.app and post the output of the following (harmless) command-line command:

ls -ale@ ~/image.jog

Cut-and-paste the output of that command back here.

I just ran into an Image file with the "Unidentified developer" warning. It's basically something in the image metadata tripping the warning. Metadata for those not famiiar is File Information that goes with the image. Sometimes when a image is constructed from other images, its metadata is included. That's known as Document Ancestors.

In Bridge I have a script to clean metadata and the image opened up in Photoshop without the Gatekeeper warning.

This thread goes into to detail and provides the script and other methods to clean out anything that might be triggering gatekeeper.

Inflated JPG File Size - Photoshop Document:An... | Adobe Community

Gene

Metadata alone in an image shouldn’t trigger a gatekeeper warning. That’d be a bug in gatekeeper.

A corrupt image file or maybe a polyglot image file might, though AFAIK jpg file formats can’t coexist with much else that’s directly executable on macOS.

It is possible to lace images with all sorts of not-image contents, but it's getting it to be directly executable that’s the tricky part.

There are a few “bad words” at the following web site, but it’s one of the better resources available for polyglot files: https://www.alchemistowl.org/pocorgtfo/

Well it is the random image (usually downloaded) file that triggers this and the document ancestors script does fix the problem. Whether it was the metadata or not, I won't debate that. I just want to provide a suggested fix that does no harm.

I'm actually running 10.13.3 and it wouldn't surprise me if it turned out Gatekeeper had a bug.

Yes, I have heard of malicious code embedded in the metadata, but as you said, it would be a tricky thing to execute.

Anyway, what I did on that one file killed the gatekeeper warning and if I know it worked, it's a good thing to let others know. The fixed image itself opens in Photoshop without a complaint.

Did you check System Preferences>Security & Privacy>General to make sure "anywhere" is enabled?

but selecting a lot from a massive folder with add hours to my workflow this way.

No it won't. Highlighting all the pictures at the same time will enable you to open them all at once.

Makes no sense! - My jpg file is not from "anywhere", it is directly from my own HD! The application pose to open it is also from apple stores!

Barney, please read the original question. You're answer is for a different problem.