OSP have a Link Report feature where you can download a csv file which you can filter the "ItemType" to be Document or Image, so you can get list of Document/Image ViewUrls. Save the selected lines with Headers to different csv file, and make sure the csv file has at least two columns. This is due to an bug in csvimporter used by OSP.

Install OSP Chrome extension (see Use Chrome extension to upload ), make sure you current tab is your OSP website and you are logged in with permission to download those URLs, open the OSP extension popup, click the "Batch  Download URLs" tab, upload the csv file, drag the ViewUrl column to map it to Url column and click the Import Button. Then you can click the "Batch Download URLs" botton and it should download those files in batches.