Sometimes after installation, some images on custom CMS pages or inside static blocks (e.g. images in the slideshow) are not displayed. First, check if images were uploaded and if correct paths to those files can be found in the source code of your page (click CTRL+U in most browsers).
If all files were uploaded and paths are correct, it means that your Magento doesn’t have access to those images because of incorrect file permissions on your server. You need to set correct file permissions for all images and folders containing images (in most cases images are stored in Magento's media/ directory). Refer to files permissions for more info.