As the thread title asks?  Even putting a image in a table that is set to a percentage does nothing.

You'll need to shrink the image in the site hosting it.

No.  The RPoL <img> tag doesn't support any other attributes besides the left/right alignment attributes.

RPoL faqs (rubbcode)

Does anyone know if the Responsive Site autocorrects for oversized images?  If so, that alone might convince me to switch...

An oversized image doesn't break the responsive site like it does the old version.

The responsive site size corrects an image that's too wide and allows its viewing at full size on a click/tap.

At least I believe that's the current functionality.  I think initially it just allowed you to independently scroll the image left/right while leaving the rest of the page intact.

Either way, a 1000% improvement over the old site's handling of the issue.

According to this https://r.rpol.net/info.cgi?action=version
Image resizing was added. But I just can't figure out how. Any help?

I believe that's a reference to the automatic resizing on the responsive site.

On the original version, if you posted an image wider than the general width of the page as the users browser was set to, the page would stretch out and the whole layout would be distorted with the user potentially having to scroll left/right to see everything (including the text) on the page.

I believe that update note you linked was regarding the current iteration of the responsive site which will automatically resize an oversized image so it fits the users screen width, and the user can then tap/click on the image to open up the full size version.

So you technically don't have to resize your images before hosting them wherever you'll be linking them from, the responsive site should do it automatically at least to the extent they don't break the usability of the site.

If you want them smaller still you'll have to decrease the actual image size prior to upload to the image host.

A roundabout way to do this is to host it on a spot like Imgur.  You can get links for different image sizes, and use those links in RPoL.