I'll quote JGC:

"Hmm, libtiff should have those dependencies as makedependencies. The libtiff.so file in it only needs zlib, libjpeg and glibc to function."

So everything else should be a makedepends entry. This should avoid requiring X to install things like samba or imagemagick.

Usually I reserve myself to medium or lower severity, but I indicate this one as high because it can be a security hole if someone isn't paying enough attention to their pacman output and inadvertantly installs X. Plus, it can be really hard to recover from an error like that.