Don't send asset data during game-play sessions.
Either use a launcher to make sure that the game assets are up to date with what's on the server before the game starts, or do the download process in a loading screen.
In both cases, I suggest you use two different servers: one from which the game clients will download the assets, and one that will be used to process the actual game-play.
Otherwise, I suggest you re-think your game design: make the image not mandatory to continue the game-play, like a player guild icon, or a decorative hat.
Textures are generally much bigger to send over the network than your usual game packets. So it would be easy for a small group of players who know when the assets are sent in game to create a situation where too many assets are sent at once to the clients, and make your server slow down to a crawl because it's busy sending images to 50% of your players, not having time to process the actual game, and send actual game packets. Like a DDOS attack. (This has happened before.)