The small picture next to your server in the multiplayer list comes from one file with one very specific format. Get either wrong and Minecraft silently ignores it.
Why it happens
Minecraft reads a single file named server-icon.png from the server root. It has to be exactly 64 by 64 pixels and a real PNG. Anything else is skipped without an error message.
What to do
- Resize your image to 64 × 64
Exactly, not approximately. A 65-pixel image is rejected the same as a 500-pixel one.
- Save it as PNG
Renaming a JPG to
.pngdoes not convert it — the file contents still say JPG and Minecraft will refuse it. Export properly from your image editor. - Upload it to the server root as
server-icon.pngSame folder as
server.properties, and the name has to match exactly, in lowercase. - Restart the server
The icon is read at boot, so it will not appear until the next start.
Remove and re-add the server in your multiplayer list. The icon appears next to the name.
PNG transparency works, so a logo with a transparent background will look right against the client's background.