You can put your images on your site and then place an html image link into your newsletter code to pull the image from your site and insert it into your newsletter. This uses the same image link as you use to insert images on a web page eg .
The difference from using such a link in an email rather than on a web page is the person reading the email has to be connected to the internet to see the image, they can't see it if they are offline. Also any sensible person who has set the spam filtering in their email program to disable external image links will not see the images at all.
For everyone to see the images they need to be embedded in the email itself. I don't think the Bravenet mailing list supports embedded images.
The other alternative is to provide links from the images eg. link to image