Preview Click Handler

(function() {
 new MultipleUpload('#demo', {
 uploadUrl: '/api/upload',
 multiple: true,
 accept: 'image/*',
 showThumbnails: true,
 onPreviewClick: function(task) {
 if (task.thumbnailUrl) {
 MultipleUpload.showLightbox(task.thumbnailUrl, task.fileName);
 }
 }
 });
})();

A hook on the thumbnail

onPreviewClick fires when the user clicks a file's preview and hands you the task, so you decide what happens. Without it the thumbnail is decoration; with it, it is the obvious way into a larger view.

What to open

A lightbox is the usual answer, but the task is yours to interpret — open a crop editor, jump to the record the file belongs to, or show the metadata you read during validation. The click already carries the user's intent, which is the hard part.