Hi Stef,
It's not a supported feature, but it should be possible to customize the code to allow this.
For example, if you look at the
MemoryNS portal, they have some code in their custom theme plugin that applies a default transparent background image whenever a logo has not been manually uploaded:
I believe that this is being done purely with CSS, with something like this:
.repository .brick-only-text {
background-image: url(/plugins/customPluginName/images/custom-background-image-name.png);
background-position: right bottom 15px;
background-size: 170px 170px;
background-repeat: no-repeat;
}
If you wanted something hardcoded to a specific upload, I believe these are the two files you would want to look at modifying:
Cheers,