Long legs. Here are the tricks to get them in camera. Lens choice along with a tweak of the point of view, you can create them on demand. It’s not that tricky once you know the trick.
The wider-angle lens works the best. The trick is to shoot up and slightly tilt the lens. You need to be careful, though, because if you get in too close the feet get large with the legs going impossibly long. For a stylistic statement, this works great, but you need a subtle look for it to be believable. Just drop your lens center point below her waistline and tilt up. You can see her legs lengthening.
The side effect benefit is that as the legs stretch, they also become a little thinner.
Her leg position – or, rather, her feet position – is critical. If the legs are apart, they should be slightly wider than her shoulders. If together it works better if they are entwined. Raised heels, either on toes or very high heels. Low heels or even midsize heels won’t work.
Another angle that works great is from above. The same principal works, get back a bit, and tilt the lens. You can magnify the effect by positioning the legs so they aim towards the corner of the frame. The lens pulls things out to the edge, making the legs longer and more slender.
Try this approach; your model will be thrilled when she looks at your camera back to see her shapely gams. Bonus, one less step in Photoshop to do.