Inventory images before replacing them
A folder can contain a cover while its audio files contain another image. Jellyfin documents external-image priority and a fallback to the first track with embedded art when no image is supplied. List both inputs before deciding that the server has simply ignored the folder image.
Change one candidate in a sample
Save the current artwork and a view of the album page. On a reversible sample, apply the documented name and location for the intended artwork role. Refresh using the operation appropriate to your installed release, then compare the result.
Keep album identity in the comparison. The intended cover appearing on a similarly named but incorrect release is not a satisfactory fix. If the server result is right and one client still differs, record that client's version before changing the source images again.
Keep image provenance
Retain where the selected picture came from and what use is permitted. An image available online is not automatically an asset you may redistribute. The practical result should explain the selected cover and its competing inputs, while leaving the original image recoverable.
Questions answered
Should I delete all embedded images as a first step?
No. Inventory and preserve them, then test the intended precedence on a small reversible sample.
Does a correct album cover settle artist artwork too?
No. Check the relevant artwork role separately.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.