You are limited to three pictures per each auction listing. Yahoo will place the first picture at the top of your listing, the second in the center, and the third at the bottom.
If you have three pictures for one auction, you have to upload them one at a time and then click done to continue placing your description with that listing.
After you get 5 feedback ratings you can use their bulk loader. It works great and you can zip all your pictures for one batch of auctions and ftp them to Yahoo. It is a great time saver.
If you're going "back" and using the same "Submitting an Item" page for each new listing, you need to DELETE the uploaded image(s) from the previous listing AND HTML links for any other images that are in your description box BEFORE you upload another photo.
Ways to get more images into your listing:
1) Do as jozi does---gang two or more photos into ONE image in your software before uploading or linking, and they will count as just one image.
2) Write HTML code for the viewer to "click on" to see additional photos (which you have hosted somewhere), something like "CLICK HERE FOR ADDITIONAL VIEWS".
3) Submit your listing with the allowed 3 images (including counters and logos), then under "Manage" click "Edit Auction Description" and write links for additional photos as an amendment.