By default, graphics commands like \includegraphics look
"wherever TeX files are found" for the graphic file they're being
asked to use. This can reduce your flexibility if you choose to hold
your graphics files in a common directory, away from your (La)TeX
sources.
The simplest solution is to patch TeX's path, by changing the
default path. On most systems, the default path is taken from the
environment variable TEXINPUTS, if it's present; you can adapt that
to take in the path it already has, by setting the variable to
TEXINPUTS=.:<graphics path(s)>:on a Unix system; on a Windows system the separator will be "
;"
rather than ":". The "." is there to ensure that the current
directory is searched first; the trailing ":" says "patch in the
value of TEXINPUTS from your configuration file, here".
This method has the merit of efficiency ((La)TeX does all of the searches, which is quick), but it's always clumsy and may prove inconvenient to use in Windows setups (at least).
The alternative is to use the graphics package command
\graphicspath; this command is of course also available to users
of the graphicx and the epsfig packages. The
syntax of \graphicspath's one argument is slightly odd: it's a
sequence of paths (typically relative paths), each of which is
enclosed in braces. A slightly odd sample, given in the
graphics bundle documentation, is:
\graphicspath{{eps/}{tiff/}}
however, if the security checks on your (La)TeX system allow, the
path may be anything you choose (rather than strictly relative, like
those above).
Be aware that \graphicspath does not affect the operations of
graphics macros other than those from the graphics bundle - in
particular, those of the outdated epsf and
psfig packages are immune.
The disadvantage of the \graphicspath method is inefficiency. The
package will call (La)TeX once for each entry in the list, which is
itself slows things. More seriously, TeX remembers the file name,
thus effectively losing memory, every time it's
asked to look up a file, so a document that uses a huge number of
graphical inputs could be embarrassed by lack of memory.
If your document is split into a variety of directories, and each directory has its associated graphics, the import package may well be the thing for you; see the discussion in the question " bits of document in other directories ".
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=graphicspath