How to add icon and thumbnail image for a Screensaver ?

I’m not sure I understand the specific goal you’re trying to achieve. Can you post some screenshots of what the images you’re trying to change?

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
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See my Feedback FB21094920. In System Settings a Custom Screen Saver no longer displays it's own thumbnail.

If a custom Screen Saver has been installed prior to OS 26 then a cached version of the thumbnail is used but a new version is never used, I've tried PNG/TIFF, .icons, .icns and .xcassets.

Thanks for the extra info.

And that’s for filing FB21094920. That’s likely to be the best path forward with this.

The behaviour you’ve described seems to match that on macOS 15. So, it’s not clear to me whether you’re reporting a regression? Or just a general issue with the API?

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
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I would not have noticed this issue in macOS 15 because I was not changing the icon, and it had been previously cached. With Mac OS 26 and the new glass icons I decided to make an icon upgrade to an App and its associated Screen Saver, that’s when I first became aware of the issue. So I suppose I’m reporting a regression, or simply “hey it’s broke, I want some glass”.

The Screen Saver docs do not mention the System Setting thumbnail, but it seems I learned to include two thumbnail files:

thumbnail.png       90x58 px
thumbnail@2x.png		180x116 px

The saver installer then takes these two files and creates thumbnail.tiff, a single file that includes these two PNGs (never knew that was possible!). When I modified the two PNGs there was no change in appearance in the System Settings thumbnail. So the installer was using a cached thumbnail, but I haven’t located where it is.

For the test saver in FB21094920 I was never able to set its icon/thumbnail, and it used the blue swirl (I assume) because nothing had ever been cached under that Saver’s name.

Thanks for your attention.

because I was not changing the icon, and it had been previously cached.

OK. But you can test this by setting up a new macOS 15 machine and trying it there. I usually use a VM for this sort of thing, because it lets me quickly get back to a ‘fresh’ state by restoring a snapshot.

it seems I learned to include two thumbnail files

Ah, that explains my confusion. Given that this isn’t documented as part of the screen saver API, it’s basically an implementation detail that you can’t rely on.

Oh, and I’d be remiss if I didn’t repeat my standard spiel:

• The current screen saver API is based on legacy in-process plug-in technology.
• This results in a wide range of performance and compatibility problems.
• If you’re interested in having a better screen saver API, one based on app extensions, I encourage you to file an enhancement request to that effect.

Please post your bug number, just for the record.

Share and Enjoy
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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"