// header widget has icon + label
HorizontalPanel panel = new HorizontalPanel();
Image imgFile = new Image(fileTypeRegistry_.getIconForFile(file));
imgFile.addStyleName(styles.fullscreenCaptionIcon());
panel.add(imgFile);
Label lblCaption = new Label(caption);
lblCaption.addStyleName(styles.fullscreenCaptionLabel());
panel.add(lblCaption);