This past halloween I did quite a bit of experimentation with projection. Used source material from both spectral illusions (Daisy and Prudence) as well as atomsfearfx (bones, jackolanterns, shades of evil and ghostly apparitions.
For Daisy - cut her general shape out of board by projecting image onto the board from approximate distance / location I planned to project from and then tracing that out. Covered the entire form in grey weathered bridal mesh, hid projector behind a tombstone with construct standing behind it to project onto. Worked perfect.
Prudence - ran nearly transparent mesh screen on fishing line at top and bottom and stretched it across our library room. With appropriate candle and chandelier lighting in the library, mesh completely disappeared and you could see our ghostly librarian 'Prudence' floating about the middle of the room. That room happens to have windows at both the front and rear of the house so people could see her from either location. Placed the projector on top one of the bookshelves and had to angle it so the bleed through fell onto a wall not visible from either window. Worked great.
Projected shades of evil onto white curtains that were already hanging in the room, simple.
In the upstairs guest window created a peppers ghost effect for ghostly apparitions. It's really challenging to figure out appropriate angles but with some trial and error - looked amazing. I ended up positioning the projector essentially hanging just above the curtain rod pointing straight down onto the floor. I used a white poster board laying on the floor to project the video onto and used a very large piece of plexiglass (purchased at orchards hardware for about $40) angled between top of window and floor at about 45 degrees. Lit the back of the room a little with standing candelabras and from the street you could clearly see ghosts floating around the middle of the room.
Also used ghostly apparitions in the graveyard - toward the back of the tombstones. Again, ran mesh strung on fishing line at bottom and top so it would keep the material fairly taught. Placed the projector at ground level shooing at a slight angle upwards so that the bleed through would predominately hit open air above the wall that outlines our front yard / graveyard. There was some image bleed onto the wall itself since I couldn't angle the projector quite as high as needed without placing the 'ghost' higher than I wanted and couldn't figure out a way to anchor the scrim that high. So for the bleed through that was visible on the wall and plants just in front of it, I used a fire and ice light and a small dim blue led flood light to wash out the area. It lit the area a little more than I would have liked but did the trick. I had tried rear projection first but couldn't hide the source projector well enough so just opted to keep the setup with front projection. Will probably rework this one a little this year.