Why is inline CSS added to images automatically? [closed]

Before you ask a question: maybe check on a other install of WP, is this the default? It is not? The problem is very often from plugins or themes. Disable plugins and switch to the default theme, current Twenty Twelve and check your problem.

The current release 3.5 and 3.4* have not this insert as default, only the img tag with path and alt attribute.