Sharkie there are tricks you can do. First is to use magic lasso or magnetic lasso in " delete from" mode which can be found in the upper left by were you would select a brush size or font size. Second is to create a duplicate layer of the picture. You can select to view and work with just the one layer. Change the image properties on the duplicate layer. Make the layer monochromatic( I believe is the word I'm looking for) or in other words a solid color. This will make it easier for magic lasso or magnetic lasso to find the true edge. Once you have it outlined you can delete the duplicate layer or deselect it. Reselect the original, from there you can go to edit and select clear. This will delete the inside portion from the picture.
Or you could send the raw file to me and I could do it for ya.
post edit thought thingy,lol
Your clock I think I know why it doesn't look right. When the clear clock panels were made and the glass affect applied (if used it looks like it was) it beveled the picture all the way around which is causing a distorted look were there upper and lower panels meet. When I did mine I think I noticed this and moved to only beveling the picture on 3 sides.