The current update of the Image Store Plugin includes a new attribute in the Store’s settings, to decide if display the watermark at bottom of the images previews, or at middle.
The previous version of the plugin inserts the watermark text only at bottom of the preview images, but in some images, a black frame with a text, at bottom of the image is not sufficient to protect it, that is the reason we’ve decided give to the users the possibility to insert a black frame, with transparence, at middle of the image with the watermark text.