Picasso had it right with this quote, part of the artistic experience is to take what is out there and change it to make it your own artistic vision. This could be changing basic elements in your art to abstracting the image. You can change the composition by narrowing the picture plane or just leaving out parts of the reference picture that clutter the composition’s general look. You can also change the composition by lowering or raising the horizon line so the viewer looks at the art from a different perspective.
An often overlooked option is to change some of the values ( light and dark ) from the original reference photo. You could change the amount of dark values in the composition. Or change an object or area to a stronger, darker value. The effect would be a difference center of interest in the composition. The photo on the left is a drawing by one of my drawing students, notice strong values of the portrait and the lighter values in the background. See what a striking drawing this makes with the stark contrast of values.
If you are in the Boulder, Co. area check out my on going drawing classes at the pARTiculars Art Studio and Gallery. http://particularsart.com/