Can't detect OpenEXR

[Robin Rowe]

I'm looking at some OpenEXR image format library detection code we've added
to our configure.in. This code was adapted from code our configure.in uses
to detect the TIFF library, but isn't working with OpenEXR. Nobody working
on our project is very familiar with autoconf. It could be something very
simple that's wrong.

AC_MSG_CHECKING(for openexr support)
  AC_CHECK_FILE(/usr/include/OpenEXR/half.h,,AC_MSG_ERROR(*** openexr header
file not found ***))
  AC_CHECK_FILE(/usr/lib/libIlmImf.a,,AC_MSG_ERROR(*** openexr dev file not
found ***))
  AC_CHECK_LIB(IlmImf,ImfApplyLut,,AC_MSG_ERROR(*** openexr dev lib not
found ***),)
  AC_CHECK_HEADER(OpenEXR/half.h,
 OPENEXR_INCLUDES="-I$prefix/include/OpenEXR";
OPENEXR_LIBS='-lIlmImf -lImath -lIex -lHalf -lz',
 AC_MSG_ERROR(*** openexr dev header half.h not found ***))

I added the AC_CHECK_FILE calls only for the purpose of testing. They pass.
The AC_CHECK_LIB and AC_CHECK_HEADER calls fail. (Each will fail, whichever
is first). The only significant thing that seems different about OpenEXR and
TIFF library is that OpenEXR is a C++ library, not C.

What's wrong? Is this even the right approach?

Thanks,

Robin