Created attachment 178393 [details]
Information panel showing only the backdrop (background) even though the poster image was embedded too in the selected file.

SUMMARY
Integrated (embedded) poster images in Matroska (.mkv) video files are not shown in the 'Information' panel

STEPS TO REPRODUCE
1. Open in Dolphin a folder where you have a  video / movie that has both a poster (cover) and a backdrop (background) artworks integrated (embedded) into it.
2. If you don't have such a file, follow these steps (inside the dashes):
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1. Find a Matroska (.mkv) file on your computer or download one from sample pages like:
https://sample-files.com/videos/mkv/
https://thetestdata.com/sample-mkv-file-download.php
2. Take a poster from here (Menu: Media -> Posters):
https://www.themoviedb.org/movie/10378-big-buck-bunny/images/posters
And a backdrop (background image) from here (Menu: Media -> Backdrops):
https://www.themoviedb.org/movie/10378-big-buck-bunny/images/backdrops
3. Save (or rename after you downloaded) the poster image as: 'cover.jpg' and the backdrop image as: 'cover_land.jpg'.
As this page tells:
https://www.matroska.org/technical/attachments.html
4. Download, install and open MKVToolnix
https://mkvtoolnix.download/
On Debian: sudo apt install mkvtoolnix-gui
5. Drag the prepared .mkv file into the "Source files:" field of the "Input" tab of MKVToolnix.
6. Switch to the "Attachments (0)" tab.
7. Drag the prepared cover.jpg and cover_land.jp files into the "Attachments to add:" field (Untick / uncheck files in the Attachments from source files:, if any).
8. Click on the "Start multiplexing" button at the bottom.
9. Switch to the "Job output" on the left vertical panel.
10. Click on the "More actions" button at the bottom and them on the "Open folder"
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3. Select the  file and open the 'Information' panel (F11).

OBSERVED RESULT
The Information panel doesn't show the poster (cover.jpg) embedded (integrated) in the .mkv file at all.
Not even after the backdrop image.

EXPECTED RESULT
I expect to see the poster (cover.jpg) embedded in the .mkv file first.
And to see the backdrop (cover_land.jpg) embedded in the .mkv file second.

Since the backdrops (background) images most of the times don't have any texts on them or are just some frames (captures) from the videos are way less helpful than the posters for recognizing what the video is about.
The priority for showing art works should be the posters first and backdrops after them.
There's enough space to show both of them if that key: value text below them is moved more towards the bottom.
So ideally both should be displayed, with the posters first.
But if for whatever reason cannot be both displayed, then the poster is more important and that should be shown, if available of course.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma:
KDE Plasma Version: 6.3.0
KDE Frameworks Version: 6.10.0
Qt Version: 6.7.2
Kernel Version: 6.12.13-amd64 (64-bit)
Graphics Platform: Wayland

HARDWARE SPECIFICATIONS
Hardware: Laptop Dell Inspiron 5770 (17" 1080p@60Hz screen)
CPU: Intel® Core™ i5-8250U CPU @ 1.60GHz
GPU 1: Mesa Intel® UHD Graphics 620 (main)
GPU 2: AMD Radeon R5 M465 Series
RAM: 8 GiB (7.7 GiB usable)

ADDITIONAL INFORMATION
On Windows, the Icaros tool (part of the K-lite codec pack) does a similar thing:
https://www.videohelp.com/software/Icaros
And when I was using it on Windows 7, it always preferred to show the posters, if they were embedded.
If they were not, then it showed a frame from somewhere in the video file.
I don't remember if Windows 7 had an Information panel, but with the help of Icaros, the poster or the frame preview was shown in front of the file, in the big status bar at the bottom when a video file was selected.