Are you refering to doing something like either of these two?
If this is what you are wanting to do, what I do is put my focus selector right on the edge of the horse/person, and the light sky behind them, or where ever the sun hits on them. Your camera will want to expose brighter because of the sky/sun, so I crank my shutter speed up to darken it. Then I take the image into photoshop, and adjust my blacks even darker. I have slr camera, and if what you have is a point and shoot camera, I'm not sure my way will work. Try it though, and then adjust the blacks in whatever program you use to edit your photos.
on photoshop you outline and cut out the horse then once all you have is a cutout you go to "Image" then "ajustments" and then "levels" and drag th levels all the way to black