The Queen's picture on the note is the watermark (Ghost image) that will appear on the back and the front of the note when tilted.
The note appears to be circulated, and so there could be many factors as to why the watermark is visible and why the extra ink is present on the note.
To me (and without looking at the note in person) it would appear that this note might have a minor ink smear on the back from the printing process. If this is the case, then the watermark could have picked up some of the excess ink (from printing plates not being wiped properly) resulting in the image appearing, (like a pencil/crayon rubbing). The flip side to that like I said, the note could have been rubbed with ink or crayon while in circulation.
As for the value, that is a tough one. The note is circulated; and the note would definitely be questioned about the smear. I pickup a few similar notes awhile back for a very small premium over face, and they were unc. What I can tell you, it is worth no less then $20, and I would be willing to pay $22 + postage for the note.
Cheers