Well, the idea is not new, but is a fair request though.
Now it is tighlty tied to the skin system, so each skin needs some tweak to show your custom pic. It's actually easy though, in the Modern skin case the solution is sort of like on the other skins:
- Open the skin's folder (if you haven't extracted to a folder yet, do it now, ask me how to if you don't know how).
- Go to the folder where all the XMLs are.
- Open the file "player-elements.xml" (on every skin this file's name changes a bit) with any editor like Notepad.
- On the 2nd or 3rd row add:
<bitmap id="winamp.cover.notfound" file="@SKINSPATH@/notfound.png" gammagroup=""/>
- ..and Save.
- Voilá! Any PNG you put on your skin's folder named "notfound" will work.
I recommend you use at least 256x256px pics, but don't get too hopefull to get rid of the little artifacts Winamp makes to the image when resizing it.. (blame the engine.. or coders in charge at that moment heh..).
JPG's are allowed too, just change the piece of code accordingly ("..@SKINSPATH@/notfound.png" >> "@SKINSPATH@/notfound.jpg").
GIF could be use too, but there will be no animation at all. This is one of the great debts of Winamp..
PS: cPro skins have a picture of their own to show no-art pics, but it doesn't affect the ML pics, so the trick is useful there too (though you need to change 2 files to set it the same).