Reducing image size in RSS only

Is it possible to reduce the image size of WordPress rss feeds parse to feedburner?

Meaning to say I still want to retain the large image size on the original post page but only display the thumbnail or medium sized image when subscribers are reading it via feedburner.

It’s very possible, but quite hard to accomplish reliably for all cases (I was working on a plugin for client to do this and more, but sadly the project was never completed).

But if you need this for specific blog that you have control over – then task can be simplified with some constrains – mainly limiting processing to attachments only.

If so:

• filter the_content_rss, extract all images with regexp;
• determine attachments IDs for images, see this question and my answer there for some helpful code;
• retrieve attachment img tag in smaller size and replace currently used version with it.