A free Photoshop tutorial for creating a spotlight effect from a normal image
Find the image you want to use and load it into Photoshop. Add a Hue/Saturation adjustment layer by going to Layer>New Adjustment Layer>Hue/Saturation.
With the adjustment open, tick the Colorize box. This allows us to edit the whole colour scheme. Move the Hue slider until it reads between 180 and 220 and lower the Lightness slider down to around -40 (or even to -50). This will make your picture dark blue.
Make a new layer above the Hue/Saturation adjustment, and using the Elliptical Marquee tool, draw a circle over the subject. Fill the selection by going to Edit>Fill>White, then press Ctrl/Cmd+D to remove the selection.
Blur the circle by going to Filter>Blur>Gaussian Blur>25, Finally set the layer blending mode to Overlay.