photoshop: how to deform?

Which version of photshop are you using, and in what language?  and for Windows or Macintosh?

But basically to transform a bit of a picture:
you can select it, using lasso or marquee tools.  Then on the menu bar go to Select, then down to Transform Selection.  You get a little box around your selection with little square handles on the sides and corners.  You can drag the corners and squish your picture around.
Additionally, you can (in Photoshop CS at least, I forget about earlier versions) click the warp button while transforming and squish around your image more organically.

Are you using CS2? because I use CS myself, and I don't have that "warp" button option. It looks like an extremely useful feature. I hope they keep it in the upcoming CS3; I'm planning to upgrade to that as soon after it's released as I can afford to.

This is something I'm quite familiar with, as most of my morphs use these techniques at some stage or another.

1. I consider the liquify tool to be a bit of a curse rather than a blessing: the amount of lumpy, crap muscle morphs seen on the net which just blast the liquify tool is depressing.

1a. The best tip for using the liquify tool is to do it gently; I tend to have the brush strength set to 10% or thereabouts and gradually add more and more distortion in small steps. Further, there are a lot of other tools which will help limit changes to other unaffected parts of the drawing.

1b. The next tip for using the liquify tool is getting the brush size right. I often find that a massive brush size, sparingly applied can add depth/size/mass to an image without distorting the pixels too much.

1c. The previous two tips help me avoid the greatest sin on liquify, which is massive pixel distortion. If you keep the pixels roughly square and roughly reasonable sizes, the morph can still retain quality (this may not apply somuch to your line drawings Gettar). If you are morphing though, and you overdo it, but like the effect, a smart blur followed by a faded out add gaussian noise (monotone) can occasionally do the job of recreating the effect of normal pixels.

2. The distort tool is an old friend and one which I still enjoy using. It can be one of the most flexible tools in photoshop.

2a. The first hint is to plan your morph or transform beforehand. On my morphs i generally cut out each muscle group on a limb and put them into a group for that limb; I can then morph each one and rearrange them freely, in easy stages. It just stands to reason that with increased mass, there might be a significant change in relationship between the three points of hand, elbow and shoulder on an arm, for example. If you have an idea of what you want to achieve, proper planning will make the work better and the result easier to get.

2b. There are occasions when the distort handles occur in locations that don't make the transform you want easy or possible. You can either chop the target apart as I tend to do, or cheat. Cheating is in transforming the part for change by rotating and then accepting the transform, when you transform it again, the bounding box will have been reset and you can use the new handles as you choose. Conversely, should you choose to rotate and distort and image simultaneously, and are happy with the locaion of the selection handles, do it in one hit: ctrl+t > right-click > select rotate > rotate to suit > right-click > select distort > distort to suit > accept changes. Try it and you might see what I mean.

3. The warp tool is awesome for photo morphs in CS2. I may be an addict and I've only really used it once. As an example of what I mean, check out the lindsay mulinazzi morph in may last thread and compare it to the annie morph: lindsay was warped, annie was distorted. Torsos are really hard to distort well, but can warp really naturally. Here's the link: http://amaz0ns.com/index.php?option=com_smf&Itemid=135&topic=4930.10

Anyway, as far as the warping technical stuff is concerned, Jed has it nailed. Hope some of this helps.