How to add a default Field when creating a Content Type? I use to add a image field every time I create any content type. Just wondering if is there any way to add this field by default when the content type is created.

I found the http://drupal.org/project/content_type_extras module which provides some additional features to content types, but it doesn't include this feature.
Not fully what you're asking. But once you have defined your image field you can easily reuse it in any content type. Since defining new content types is not something you do every day, this shouldn't be to much of extra work.