diff -ur iscan-2.26.2/configure.ac iscan-2.26.2.new/configure.ac
--- iscan-2.26.2/configure.ac	2014-01-27 13:37:26.782024452 -0500
+++ iscan-2.26.2.new/configure.ac	2014-01-27 13:36:47.738024120 -0500
@@ -274,6 +274,9 @@
 		  AC_HELP_STRING([--enable-$1],
 				 [ensure support for the $3 file format]),
 		  [if test "x$enable_$1" != xno; then
+		      if test "x$4" != xno; then
+		         PKG_CHECK_MODULES($3,[$4])
+		      fi
 		      iff_header="`echo $2 | $as_tr_sh`"
 		      AC_CHECK_HEADERS([$2])
 		      if test `eval echo '$ac_cv_header_'$iff_header` \
@@ -284,9 +287,9 @@
 		  [AC_CHECK_HEADERS([$2])])
    ])
 
-ISCAN_FILE_FORMAT(jpeg,jpeglib.h,JPEG)
-ISCAN_FILE_FORMAT(png,png.h,PNG)
-ISCAN_FILE_FORMAT(tiff,tiffio.h,TIFF)
+ISCAN_FILE_FORMAT(jpeg,jpeglib.h,JPEG,no)
+ISCAN_FILE_FORMAT(png,png.h,PNG,libpng)
+ISCAN_FILE_FORMAT(tiff,tiffio.h,TIFF,no)
 
 
 dnl  Support for performance measurements.
diff -ur iscan-2.26.2/frontend/Makefile.am iscan-2.26.2.new/frontend/Makefile.am
--- iscan-2.26.2/frontend/Makefile.am	2014-01-27 13:31:09.488021241 -0500
+++ iscan-2.26.2.new/frontend/Makefile.am	2014-01-27 13:37:50.065024650 -0500
@@ -37,6 +37,7 @@
 	-lltdl \
 	@GTK_LIBS@ \
 	@GDK_IMLIB_LIBS@ \
+	@PNG_LIBS@ \
 	$(top_builddir)/non-free/libesmod.so
 iscan_SOURCES = \
 	$(iscan_source_files)