Many question has image url instead of direct image. Is that right practice to edit those old post and replace url to direct image?
While the posts are usually better with inlined images, be aware that uploading copyrighted images is a breach of the Stack Exchange TOS. Images hosted on Stack Overflow is released under the Creative Commons Attribution-ShareAlike 3.0 Unported license in the same way as any text. You should ask the original poster in a comment before uploading any image that isn't yours.
Directly from the license text:
With this said, U.S. copyright law have a special clause called Fair Use which allows you to use copyrighted content without permission in some cases. It may be possible to upload images under this exception, but it is not applicable for all countries.
The copying is probably considered carried out in the country the user is in. In Sweden, where I am, images are almost never covered by any fair use clause and even very small thumbnails have been considered a copyright infringement in courts.
Sure it is! This usually occurs to new users who are not allowed yet to post images...
Just be sure to read over the entire post and fix any other problems you come across... Make sure is not just a minor edit...