[jax]

hahaha you're so sad
There are addons and systems in place that others server use to make sprays more secure
There are addons that enable the picture to be tagged with the STEAM ID: of the person who sprayed it, and allow the sprays to be vetted before being accepted.
There are addons that don't even use the current spray system GMOD has on by default.
There's more than one way approach something

Letting a player pick any file on their computer to send to every player on the server isn't a great idea.
Even with an addon that forces you to use image URLS, we've all seen images on Discord that cause crashes or can redirect to things that are not images.
..
We can get into some serious trouble for letting people put some images on the wall.

I already talked about both of these options. The tagging with STEAMID is done through an addon called SprayMon, but still suffers the same security issues. There have been attacks in the past that use sprays as an attack vector for remote code execution. That's not happening.

SprayURL and similar addons are more secure since you can only use URLS (i.e. replaces the default spray system as you said), but we still have the glaring problem of letting random people spray anything they want on the wall. During the short periods where sprays WERE enabled, the amount of people reported for spraying porn on the wall is enough to cause major issues. Kids play on these servers.

Having a set of "preset" sprays would be a good idea, but I'm not aware of any spray system that can do this. However, Garry's Mod already has this "preset" sprays feature. All of the default sprays you can pick from in the settings are visible to other players (like the target spray)

There's always the option of limiting it to donors / approved players with a pre-approved jpg list. Or make it a novelty item, like the vape, that is found in Crate of Dumb Garbage. Make a SWEP that emulates "sprays". But if there are no developers then I guess that's a moot point.