Not a fully automatic method but if the border isn't part of the actual picture you can try this. Click on the first picture then go to 'Picture Tools', 'Picture Border' and click on 'No Outline'. This should remove the border from this picture. Back on the Home tab, make sure the picture is still selected then double-click the 'Format Painter'. Now go through the document, click on each picture in turn and the borders should go. At the end, click once on the 'Format Painter' to release it.