For classifieds you can upload maximum 5 pictures, for events you are allowed to upload one picture.
While you enter your information on the "Post Form" you have the option to include a picture by selecting the "browse" button.
Search in the directory of your computer to find the picture. You can view the uploaded picture in the preview page.
The format of the picture should be jpg, gif and png. The normal size of a picture is about 20 KB. If you have problems to include a picture it might be the wrong format or the wrong size.