This image was shot in a RAW format and so after making the necessary adjustments I opened the image. You can either set the color balance before or after selecting your object within the picture. I chose to do it after I had selected my object because I feel it is better to work with individual objects rather than a entire scene. This is merely personal preference and is up to you. Try and match the color to the same white balance and other necessary settings to the image you will be placing your selected objects into later.
The next step is to get your polygonal lasso tool (L) and trace the outline of one of the girls. Once the girl is selected, go to Select, then Refine Edge. Choose a black background to go around your picture while you are working with the tightness of your cropping around your selection. You may have to contract or expand you selection a bit before you add a bit of radius and feather, then click Ok. Select inverse, then press delete to get rid of everything else in the picture.
Your window should look like this. At this stage go to Filter>Sharpen and Add Noise. Try only about 2% or less.
Save your file and place it into the photo your are transferring your selections to. Free transform the image till the size is right and repeat steps 1-3 with the other objects you will be placing in the photo. Remember to hold the Shift key while you are doing this so that you don't stretch you object. Once your objects are in, you may want to add a drop shadow or create a new layer, choose the Brush tool and lower the opacity. I think for this I lowered it to 13% and brushed my shadows in. I also slightly desaturated the girls to make their colors a bit more consistent with the photo. Look for highlights in the image that "pop" too much and darken them a little. In this photo I darkened top of the steps slightly.
Keep playing with the different layers and blending modes to create the desire effect. Below is the finished product.
If you have any questions please feel free to ask!
