Note that tiff 4.x provides libtiff5 and libtiff5-dev, while tiff 3.x
provides libtiff4 and libtiff4-dev.  This may seem confusing, but it
is just because the shared library versions and the software versions
don't happen to be the same, nor is there any expectation for them to
be the same.

Until the libtiff4 -> libtiff5 transition occurs after the release of
wheezy, a new temporary package called libtiff5-alt-dev is being
provided.  This package installs include and library files for
libtiff5 (tiff 4.x) in an alternative location with pkg-config files
that point to it.  You should only use this package if you need to
depend on libtiff5 development files while also having libtiff4-dev
installed on your system.  This package will disappear when
libtiff4-dev is removed from the archive.

The most common use of libtiff5-alt-dev will be as a build dependency
for a debian package that has a direct dependency on libtiff5 (for
example, to get bigtiff support) and an indirect dependency on
libtiff4-dev.  In this case, you can have your package specify
libtiff5-alt-dev instead of libtiff5-dev as a build dependency.  If
your package finds the location of libtiff headers and libraries with
pkg-config, then all you will have to do when libtiff5-alt-dev
disappears is to change your build dependency to libtiff-dev, which
will then point to libtiff5-dev.  For an example of a package that
does this, look at vips.  Note that if you link use this package, your
executables or shared libraries will include an rpath that points
/usr/lib/<arch>/libtiff5-alt.  This is harmless since no actual shared
libraries will live in that directory, but it is a side effect of
having libdir set in the libtiff.la file there, which is needed for
libtool to link with the correct -ltiff.  This situation will cause
lintian errors, but the problem will go away after the libtiff
transition is complete.

 -- Jay Berkenbilt <qjb@debian.org>, Thu, 24 May 2012 15:50:07 -0400