After modifying an image's metadata in AEM Assets, the XMP metadata is not written back to the image.
In AEM (CQ) 5.5 and later, changes to the metadata of an asset are written back to the original binary as part of its XMP data. The AEM Metadata write-back workflow handles this process. The workflow uses the XMPWorker Linux fragment, which is a 32-bit native executable application that AEM runs on the OS shell.
This application is also used to optimally extract the existing XMP metadata from renditions. If the writeback fails (returns a WARN message in the server error.log file) on 64-bit Linux, your OS may not have 32-bit dynamic runtime environment installed to run 32-bit executables on 64-bit Linux.