Create a Wordpress Template

I need some changes to an existing website. I have this WordPress blog called StrikeBuys ([login to view URL]) I use a lot of images from external websites in the posts. I want a plugin that will scan all posts and find the external image links. It should upload the image to my WordPress media folder and update the original post with the new link by replacing the old link. I want this plugin to run whenever a new post is published or an existing post is modified with another new external image. There are already so many plugin on WordPress which do this. But all of those cause 404 error or show 'Bad request. The browser could not understand the request sent to the server' error. I'm not sure what is happening. I want a plugin that does a neat job.