In order to make patterns from photographs, you will have to have some sort of photo editing software.  There are several different ones out there.  I use Corel Draw.  You can try Paintshop Pro which is available for download at Jasc Inc.'s web site.  It's gotten a little pricey lately, so if you have another comparable graphics program, you can probably use it instead.  For instance you can do most of the process with MGI Photosuite SE.  However you can not turn it all to black and white.  You have to instead use a feature called cartoonize.  This will change it to black, white and orangish.  That can also work fine for pumpkin patterns.
    This is a description of how I do it with Corel Draw.

    The first thing I do is to crop the picture to the area I want it to be.  For a portrait, that is usually the head and just a bit of the shoulders.  Then resize your picture to approximately 600 pixels.  This is a good size to work with.  The next thing is to trace around the head.  Trace around the head, hair and shoulders.

Then you can go back and black out the entire background.  Anything not in the pattern should be black now.  The next step is to convert the photo to grayscale.  To do this go to "Image" menu, then down to "Convert" and finally to "grayscale (8bit)."

Now depending on the picture quality, you may have to adjust the contrast/brightness to make the features a bit better.  Go to the "Effects" menu, then to "Color Adjust" and finally to "Brightness-Contrast-Intensity.  Here you can play with the numbers on both until you get them where you want them.  The one below is a change from above with Brightness - 16, Contrast - 22 and Intensity - 8.

Next you will do what is called "Posterize."  Go to the "Effects" menu, then select "Color Transform," and finally Posterize.  This one is at level 5.  Again, you can play with it till it looks good for you.  You may have to undo it and go back to the Color Adjust, if there is too much brightness in it.  This one should probably have been darkened a bit and posterized at 6.  But it still works.

Now you need to go back and clean up the lines.  If you are only going for three colors an a bit less detail, you will fill in to make three colors here also.  Basically you will just use the paint tool on a round brush setting and smooth it out.  Also it may be impossible to get a perfect match on the color.  In this case you can use the color fill tool and make it a bit different color, but all matching.  That is what I did below.  You can notice a slight change in the colors, and that it is only four colors now.  The other thing that must be done here is to make sure that you can carve the pumpkin.  The white area is the area that will be cut completely out.  If you notice above, If the white were cut completely out, the left eye would fall out.  the area on the edge of the mouth would also be very weak.  That is why there is very little white below.

Now go to the "Effects" menu and select Color Transform again.  This time click on "invert."  This gives the picture a negative effect.  You will be cutting out the black completely on this pattern.  This will save you a lot of ink when you print it, and will be easier for you to transfer to your pumpkin.

That's it.  This is your pattern.  I recommend printing a low  quality, small version of the photo before you invert it.  This will give you a guide to look at while you are carving and keep your eyes adjusted right.  Good luck with what ever design you pick, and have fun carving it.
Click here to see the final result of this pumpkin.

Also if you want to look at PhotoPaint instructions and a three color design, check out Pumpkin Wizard.