I have found a very handy small module, which allows me to insert image into the content. The size of the images is also very well under control. See this howto.

For Drupal 6 there is the handy image file filter module to insert images into the content.

Update: the evolution of the module is very fast, and the features are also changing. The usability is improving, but some hints below may become misleading in time.

After the setup, you just have to upload the image file to the node as an attachment, set the orientation, and that's all. Look:

IMGFilefilter.png