undertow, thanks for your response.
I should have known to paste my ./configure setup in the post, but I didn't . . . so here it is:
./configure --with-mysql --with-xml --with-gd-dir=/usr --with-png-dir=/usr/local --with-jpeg-dir=/usr/local --with-zlib-dir=/usr --with-apxs
All of the --with-*-dir directives are pointing to the correct directories . . . I've double checked to make sure the libraries are there. I scrolled back through the output of ./configure and discovered that I was getting "checking for GD support... no", which seems quite odd since I'm specifically telling it where to look for gd.
So . . . I deleted the entire source directory (I've been using make clean before trying to ./configure and compile again, but wanted to be on the safe side) and tried again. With the same ./configure, I got the same "checking for GD support... no".
Somewhere in my searches I found someone adding a "--with-gd" to their ./configure, so I tried that:
./configure --with-mysql --with-xml --with-gd-dir="/usr" --with-png-dir=/usr/local --with-jpeg-dir=/usr/local --with-zlib-dir=/usr --with-apxs --with-gd
The relevant output:
checking for GD support... yes
checking whether to enable truetype string function in GD... no
checking for the location of libjpeg... yes
checking for jpeg_read_header in -ljpeg... yes
checking for the location of libpng... yes
checking for png_write_image in -lpng... yes
checking for the location of libXpm... no
If configure fails try --with-xpm-dir=<DIR>
checking for freetype(2)... no
If configure fails try --with-freetype-dir=<DIR>
checking for FreeType 1.x support... no
checking for T1lib support... no
checking for gdImageString16 in -lgd... no
checking for gdImagePaletteCopy in -lgd... no
checking for gdImageCreateFromPng in -lgd... no
checking for gdImageCreateFromGif in -lgd... no
checking for gdImageGif in -lgd... no
checking for gdImageWBMP in -lgd... no
checking for gdImageCreateFromJpeg in -lgd... no
checking for gdImageCreateFromXpm in -lgd... no
checking for gdImageCreateFromGd2 in -lgd... no
checking for gdImageCreateTrueColor in -lgd... no
checking for gdImageSetTile in -lgd... no
checking for gdImageSetBrush in -lgd... no
checking for gdImageStringTTF in -lgd... no
checking for gdImageStringFT in -lgd... no
checking for gdImageStringFTEx in -lgd... no
checking for gdImageColorClosestHWB in -lgd... no
checking for gdImageColorResolve in -lgd... no
checking for gdImageGifCtx in -lgd... no
Just to be on the safe side, I tried recompiling gd (with the test programs this time), and still got the same response. gddemo spits out the demoout.png just fine, so it doesn't appear to be a problem with gd.
I'm going to see what I can find about compiling gd as a module now . . .