Custom sprite won't download

[PsycoDaD]

I am trying to add our clan banner to a map or 2.
I'm just using my username for now.
I successfully edited the map entities and if the
accompanying sprite file is on ur PC u can see the banner.
If the sprite is not on ur PC u only see's a black box with spots or something.
So my question is how can we force the server to upload the
sprite to clients so they all will see it too.