When you're posting an image make sure you enlarge the one in the album, right click it and choose "Copy image address" (or just "Copy" if you're mobile). Slapping a .jpg or a .png at the end of the album URL (has the /a/ tag in it) will still make the preview unusable. I've fixed your last couple of entries but try doing this yourself next time. If you can't see the preview yourself neither can others.