Backup Contact Pictures is a Mac app that can export and import all of your contact pictures to and from a folder. When exporting, the contact's name is used for the file name of the image. When importing, the images will be assigned to all contacts whose name does match the image's name. The app can also bulk delete all contact pictures.
For the export, the JPEG format is used. The import function supports all common bitmap formats. An activity log shows you the results of each bulk operation.