How to modify the source code that also collected data used by the proxy server were stored on the server GAE? (optional: for 30 days? - Because there are limits...)
And... Sorry for my english, but you know what I mean?
For example, to the entry on the website http://kw25net-proxy.appspot.com/www.evisibility.com/images/google-bot-450.jpg also save it on the Google App Engine server (Blob?).
I am concerned mostly about image (somewhere up to 1 megabyte)
The zip file pointed by the link you've provided is a packaged version of Mirrorrr by Brett Slatkin.
As stated by the project page, Mirrorrr is a "Google App Engine application that Mirrors the content of URLs you supply. Rewrites the fetched page to mirror all content, including images, Flash, Javascript, CSS, and even favicons. You stay within the cache at mirrorrr.com when you follow links. Useful for pulling load off of slashdotted servers. Also can be used to anonymize web access."
MemCache is used as the backend technology to cache the requested content. So data is saved locally on Google App Engine servers. However, it is saved in "memory", not in the datastore.
If you were looking forward to improve the performance, it looks like this is already handled by the product. :-)