Change 991777 had a related patch set uploaded (by Dreamy Jazz; author: Dreamy Jazz):

[mediawiki/extensions/MediaModeration@master] Send email if file is uploaded that is already a match

https://gerrit.wikimedia.org/r/991777

Change 991777 merged by jenkins-bot:

[mediawiki/extensions/MediaModeration@master] Send email if file is uploaded that is already a match

https://gerrit.wikimedia.org/r/991777

Change 993499 had a related patch set uploaded (by Dreamy Jazz; author: Dreamy Jazz):

[mediawiki/extensions/MediaModeration@wmf/1.42.0-wmf.15] Send email if file is uploaded that is already a match

https://gerrit.wikimedia.org/r/993499

Change 993499 merged by jenkins-bot:

[mediawiki/extensions/MediaModeration@wmf/1.42.0-wmf.15] Send email if file is uploaded that is already a match

https://gerrit.wikimedia.org/r/993499

Mentioned in SAL (#wikimedia-operations) [2024-01-29T14:54:07Z] <Dreamy_Jazz> scap backport is also backporting 993499 for T355357

I will write suggested QA steps in a few hours.

Suggested QA steps which need a local wiki:

1. Enable email support on your wiki so that you can view emails, if not already enabled.
   1. To set-up email support for MediaWiki-Docker, you can follow the steps at https://www.mediawiki.org/wiki/MediaWiki-Docker/Configuration_recipes/Mail_handling to add Mail hog to your MediaWiki-Docker instance. You should add the code listed in that page to the listed files and then down and up your MediaWiki-Docker instance.
2. Upload a test file to your wiki
3. For the filename of the file you uploaded in step 2, note down the filename after replacing any spaces in the name with _ and removing the File: prefix.
4. Define $wgMediaModerationPhotoDNAMockServiceFiles in your LocalSettings.php as the following replacing <file> with the filename from step 3. If you already have a definition of $wgMediaModerationPhotoDNAMockServiceFiles then remove it.

$wgMediaModerationPhotoDNAMockServiceFiles = [
	'FilesToIsMatchMap'	=> [
		// change to false if you want IsMatch to be false
		'<file>' => true,
	]
];

5. Run ./maintenance/run MediaModeration:scanFilesInScanTable.php --use-jobqueue --verbose
6. Define the following in your LocalSettings.php, if you don't already have it there:

$wgMediaModerationRecipientList = [ 'admin@wikimedia.org' ];
$wgMediaModerationFrom = 'no-reply@wikimedia.org';

7. Open the email server for your wiki (if you use mail hog / did step 1A then open http://localhost:8025 ).
8. Verify that an email for the file you uploaded in step 2 is in the inbox
9. Upload the same file from step 2 under a different filename. Changing the filename can be done by modifying the Destination filename field in Special:Upload. Also check the Ignore warnings checkbox before uploading.
10. Go back to the email server for your wiki and verify a new email has appeared that only details the filename for the file uploaded in step 9.

I have verified that the new code has been implemented and is functioning and displaying as expected...
Below you will see a series of screenshots that show the sequence of the Inbox beginning with 1 email and then ending with 2 emails , both with the same SHA-1 but different filenames for the same uploaded image.
Thank you @Dreamy_Jazz.