Why is it that on some images, if I magic wand and delete, or use the eraser, I get a transparent hole or background, but on others, I get a black color? How can I get a transparent background if my source is a JPG that is leaving a black background instead?
You can also after making your careful selection of the area inverse the selection (that will chose the part you want) and do a copy and a paste. This will cause a new layer to be made of just the selection on a transparent background. You will still have the original below that you can use to clean up any areas that are missing. You then can output the file in a transparent file such as a PNG or Giff which will allow you to use it transparently in a website. Or if you do a mask of the layer you can use it transparently in After Effects. In either case when you are finished you can chose to hide the unwanted layers or merely delete them.