Two things I see which may help a bit to lower spam is No-Double posting rule and a word/character minimum to post a thread. What does that mean?
Basically, until someone else posts in a thread, you are not allowed to make a new post. If you wish to add more information or correct yourself, then you use the edit button (shocking concept, I know, right?!) That means someone else has to participate in the conversation before you make a new post.
However, since I know at times you may want to add something later on and it wouldn't make sense to combine it into an old post. For example, I have a thread of my CAWs from WWE 2k19 and while people like my posts when I make a CAW they like, not every time someone replies. So if I make a new character I want to show off, then, of course, it would likely be a separate post. That is why I suggest there should be leeway if another post isn't made within a certain timeframe. Let's say 12 hours (half a day) or 24 hours (one whole day) which I think the later may be a bit better to prevent spam.
So to summarize:
You can't make back to back posts unless 24 hours have passed. if you need to fix or add something, use the edit button for what it was designed to do!
Then, to put it as plain as possible, a word limit or character limit may be helpful. That way we won't have threads that are only an image or just one or two words as its opening post. Sure some threads are self-explanatory in nature, but it'd be better for the post to have even a tiny bit of substance to it than just one word.
Those two rules would likely help prevent spam and trashy threads. I could also mention things like... Not making the exact same post back to back (and changing capitalization or punctuation does not count), or don't make threads dedicated to shitting on fellow forum members, but let's start with those two.