Freatured image is not responsive on mobile phone

Sorry to pitch in here but I think I’m having the same issue, but with the Dazzling theme. For some reason some featured images (uploaded to slider width) are not responsive on mobile phones. I already posted about this issue in the Dazzling theme forum but I haven’t got a response so far so I thought I’d check the Sparkling forum to see if anyone has the same issue. Please check out screenshots of the issue on my original post here. Anyone have any suggestions?? I have been stalling the launch of my new site for two weeks since I can’t for the life of me figure this out… THANKS!!!