Click on the picture and scroll down. There will be an option to "Delete Photo", and then click submit.
I was doing some gallery work and I saw the "no thumbnail" icon in your gallery, so I deleted that. I also approved some pics to your gallery, so you still have your old ghost knife pic, the new pics, and the "no thumbnail" icon is gone. Your gallery should be ok now; if it's not the way you want it, let me know, and you can delete any other pics that you don't want also.