UBB.threads v7.6.1 introduced a feature which compresses images uploaded as attachments, the compression code is similar to the coding utilized in the gallery.

From the v7.6.1 Changelog:
[NEW] Attached images can now be automatically resized at the time of upload.
[NEW] Attached images can now be automatically compressed at the time of upload.
[NEW] New image "Attachments" page has been added to the Control Panel to control the size and compression of image attachments.

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