The form is another familiar image in every printed and online catalog. I have created quite a few (150? 200?) forms in the last few years, and there is no easy way to create these files. There isn’t a Photoshop action or a script to create the effect.
The photographer will shoot the apparel on a mannequin, then turn it inside out and shoot the interior separately. The retoucher’s job is to clip out both files and insert the interior layer in the back, and mask and bend that layer to fit.
I use the Warp tool to bend the interior, but I guess the Liquefy tool could also be feasible. I usually clip out the label and add it as a separate layer, so that it isn’t part of the warped interior.
T-shirts and polos are relatively easy, but scoop necks can be troublesome, just because there is more of the interior area to accurately bend. And what is worse than creating a scoop neck form? Tank tops. Warping the straps to match up with the top layer can be a real challenge.