Hi
There are several ways of attaching or enclosing images to an email.
You can, for instance, click on "Photo Browser", top right within your new message. This gives access to all your iPhoto and Aperture images any number of which can be dragged into the email. Having done so, you can select the size from small to large - bottom left of email. The largest has the least compression.
In both iPhoto and Aperture, you can, within these apps, Select "Export" and from the drop down menu, choose any degree of compression or none. "Export as Original" means no compression. You should export to the desktop and insert into email from there.
If your image(s) is/are somewhere else on your Mac, you can select them and drag or copy them into email.
Yes, you can attach images so you don't see them. By whatever method you choose for securing your images (as above), place them in a newly created Folder on your desktop and the attach the Folder. Only the Folder is seen.
Summarising all of the above, the sure way of avoiding compression is to Export from iPhoto/Aperture "As Original" to a new Folder on your desktop and attach to email in usual way.
I think that covers your questions. If not, come back.
Ian