Captchas work well for telling humans from bots for the purpose of denying automated/scripted access. But here a simple IP-based blacklist works well, because of how many bots now live on Amazon's properties and some such.
You don't need a captcha to filter out bot spam. That's a massive overkill.
stopforumspam.com works well. You can combine it with a simple keyword based filter, have it tag hits with a cookie, temporarily blacklist the IP and then filter them out based on that as well. Auto-submit it to stopforumspam too. Obviously, also have whitelisting in place, e.g. to let through existing customers, previously cleared posters, etc.
For bonus points, first-time posts that look OK may be put into a "shadow ban"-ish mode, whereby they are visible to the posters and mods, but not anyone else. Until they are cleared. This works equally well.
The bottom line is there's no spam that doesn't try to promote something and they aren't likely to target just you, so there's always a keyword/URL you can latch onto, and it also makes sense to participate in a distributed monitoring framework to piggy-back on each other's first hits.
"there's no spam that doesn't try to promote something" is, unfortunately, not true. Or at least, some spam plays the long con. On sites where karma or social graph confers advantage, bots will harvest one or both through low-effort, high-payoff posts. Various disinformation and distraction campaigns may sell only confusion, discord, or volume of content. And if it's the graph itself or specific connections which matter, ossiby for hishing, recruitment, or other compromise, you'll see other behaviours.
Not all media manipulation is commercial. Not by a long shot.
Captchas work well for telling humans from bots for the purpose of denying automated/scripted access. But here a simple IP-based blacklist works well, because of how many bots now live on Amazon's properties and some such.
You don't need a captcha to filter out bot spam. That's a massive overkill.
stopforumspam.com works well. You can combine it with a simple keyword based filter, have it tag hits with a cookie, temporarily blacklist the IP and then filter them out based on that as well. Auto-submit it to stopforumspam too. Obviously, also have whitelisting in place, e.g. to let through existing customers, previously cleared posters, etc.
For bonus points, first-time posts that look OK may be put into a "shadow ban"-ish mode, whereby they are visible to the posters and mods, but not anyone else. Until they are cleared. This works equally well.
The bottom line is there's no spam that doesn't try to promote something and they aren't likely to target just you, so there's always a keyword/URL you can latch onto, and it also makes sense to participate in a distributed monitoring framework to piggy-back on each other's first hits.