Clients can downloading images from your site using the following methods:

Within Galleries
To allow clients to download images from within a gallery you must select the Zoom and the Zoom is Downloadable options within the Presentation & Protection section just prior to upload. This will allow clients to download one image at a time. For added security, you may password protect the gallery if you have this feature.

Download Asset
Use the Downloads asset to allow clients to download a group of images quickly. To use this feature, you need to create a page and add a Downloads asset to it. Once completed, you must save your group of images into a zip archive and upload it into the Downloads asset. You may also password protect a download.

FTP
This is probably the most complicated option but if your package includes FTP access, then you may upload images into a your FTP folder and provide individual links to each image (we do not allow directory browsing) or include your own HTML index page which includes those links. Alternatively, you may zip up all the images into a single file and provide your clients a link to it.