Foswiki has support for standard Blogs (with pictures, filtering, etc), stored as separate document forms through BlogAddOn.
However this would usually assume that contributors should register, and this would not support HTML-only (generated) production.
Thus the following idea:
use simple JQuery/Ajax and a non-authentificated fast script with per-IP and minute limitation (e.g. max 5 comments per 10 minutes per IP) to allow to contribute
enable simple validation of comments to be able to easily kill unsuitable comments
does not follow the JQuery Coding Standards (but following them leads to non-functional script) and doesn't apply the onsubmit at runtime.