The current image URL (http://www.festivals.ie/images/banners/love-festivals-299-250.gif) does a 302 redirect to the actual image URL (http://www.festivals.ie/static/UO8FTf3ztOtMK2ArNFiVkIeKI2DqX13KcoktytQF1Q6.gif).
I suggest setting og:image
to the actual image URL:
<meta property="og:image" content="http://www.festivals.ie/static/UO8FTf3ztOtMK2ArNFiVkIeKI2DqX13KcoktytQF1Q6.gif">
(This is really a guess since I'm not able to test this at the moment.)