You will have to host them here on Auctiva or another photo host and then insert them using the HTML code for the image.
For example - I use photobucket for my hosting - so the code that I would use would be...
(img src=http://img.photobucket.com/albums/v51.angelsblue/imagename.jpg)
You would have to replace the () with <>.
After the img src= you would add in the image URL for your photo where ever it is hosted.