What you'll need:
A picture printed on plain paper
Knife or scissors
self-levelling gel or tar gel
sponge with scrubby side, if possible
Print out an image onto regular plain paper. The cheaper the better. Pigment inks are best but are not necessary. Any regular print will do. Any true blank area will not show white in the final. So remember that when choosing your image and choosing what to show and what not.
Cut down your picture (if necessary). Leave a bit of a border. You'll see why. You can always cut down the image after its gel application.
Tape down your image (leaving a bit of a border around the true outside of your image). It's best to tape the paper down to a non-porous board to allow for drying.
Take a spatula and coat the picture with the gel in one smooth, even and not too thick coating. Try to minimize air bubbles as these will stay. Do another pass or two to smooth it out if necessary.
Once dry the gel should now appear see-thru unlike the above. The milky look means it still isn't dry. Drying will depend on humidity in the air but be prepared to wait several hours. Repeat and coat the picture with another application of the gel. This helps with Step 6.
Once the 2nd coat is dry remove the tape (it helps if you score the paper or even just cut the picture away as close to your tape as possible). Wet the picture and your sponge. Start rubbing the back of the picture in a circular motion to remove the paper. Don't rub too hard or have any debris under the picture or folds as this will remove the pigment. Unless you want that look! Wash the transfer when you've got the paper off just to clean it up.
Now hang to dry. Because you left a little bit of extra space around the picture you don't have to worry too much about your hanging method leaving any indentation.
When dry you can apply your transfer in any way you like. If you're applying it to a panel then any type of binder medium will work to adhere it.
Enjoy your new photo transfer!