I know exactly what you mean, and some forums have it built in from the start.
Pretty much giving the option for users to hid pictures or content to only be displayed when a user decide to see it.
Sadly though SMF doesn't have this function built in, maybe there's some sort of plugin though that is similar to this function, and in all honesty I wouldn't mind if there was one. But with addons and mods usually comes the issue of stability. It usually doesn't take much or long before the forum runs into issues because of a broken mod, and with time the forum gets updated to a newer version, and it's not always it works smoothly.
If there's a good option we could see, but no promises really, we have tried to keep this forum as low as possible on mods for increased reliability.