You can post more images (up to 3 additional images). All you need is to put the direct URL to the images.
One of the ways is to use a free service at ImageShack. No registration is required and this service is absolutely free.
Here are the steps to upload your images:
1) Go to http://www.imageshack.us
2) Upload your image (select image and click "start upload!")
3) Copy "Direct link to image" URL
4) Paste the "Direct link to image" URL into our post classified ads form.
Please note if you upload multiple images, you can find direct URL in "Get links and Codes for All Images" section located at the right-bottom corner of the page, as it shown in picture:
or each image separately by copy-paste direct link as shown below: