I have a photo with of a girl wearing white dress the background of the image is white. I just want to remove only the background not the white color of photo. How I can do this?
If you want to do it automatically, you need to adjust the tolerance until it recognizes the edge of the dress. You also need to make sure you use "contiguous" areas so that it doesn't select every isolated section of that color.
If the colors in the background are too inconsistent for this to work, you can try using the magic wand selection to outline the dress and see if it properly snaps to the edges.
If the edges are still not clearly defined enough, you will need to resort to matte painting out the background. I generally do this by copying it to a second layer, putting a brightly colored layer underneath (typically red, but any bright color not found in the image works well) and then use the eraser brush to remove the background from around the dress.