- Go to Setup> Data Management > Data Export.
- Click Export Now
- Check Include images, documents, and attachments.
- Check object(s) containing the images you'd like to export.
- Click Start Export.
- SF will email you once the export is done.
- Click the link in the email.
- Within 48 hours, click download next to the file name and save it locally.
- The zip file will have following components:
- Attachment csv file - This will have a Attachment Type column, referring the IDs of image/jpeg type attachments.
- Attachment folder - Attachment IDs filtered from csv file can be retrieved from this folder. This folder will have all types of attachments, like submission xml as well. So, filtering will be required.
For more details you can refer this Salesforce article.