All JPGs are at least 450px on their shortest sides. I added some CSS
dl.gallery-item {min-width: 300px;}
and it resized them without pixelation but I’m afraid I’m breaking the responsive aspect of it—don’t want these thumbnails to be unreasonably sized on a mobile platform. Something has got to be telling the gallery to resize this file but I can’t find a plug-in or any additional code that would be doing this. I’m working on a local installation of cyberchimp’s Responsive Theme, otherwise I’d paste a link.