When you use the "Email this file" option in the tasks pane it gives you the option to reduce the size of the images. (see attached image)

Make sure you are selecting the correct option.

Either "Make the my pictures smaller" or "Keep the original sizes".

My guess is you are choosing the "smaller" option, hence thats why they are in kb's.

However, if you insert or attach a picture directly into your mail it will retain the full original size.