How to install ImageMagick on 10.6 (Snow Leopard) using a precompiled binary (without a package manager)?
Search for an old version of the binary ImageMagick release named "ImageMagick-x86_64-apple-darwin10" that runs on 10.6.8, for example:

http://tools.robodoc.net/tools/imagemagick/ImageMagick-x86_64-apple-darwin10.6.0.tar.gz

Download and extract the files.
Move the ImageMagick-6.6.7 folder to your home folder.
Start terminal and execute this command: $ export MAGICK_HOME="$HOME/ImageMagick-6.6.7";export PATH="$MAGICK_HOME/bin:$PATH";export DYLD_LIBRARY_PATH="$MAGICK_HOME/lib/"
Ready