LinuxQuestions.org - "libpng missing" on xvidcap compilation ( Slack 10.2 )

Hi all

I'm using Slackware 10.2
I have problem with LIBPNG. Whenever I try to complile a program that needs it I get errors of libpng missing, e.g. ./configure result of XVIDCAP:

Code:

checking for zlibVersion in -lz... yes 

checking for png_set_filter in -lpng... yes

as you can see lpng here is a go, but "make" outputs the following error:

Code:

gcc  -g -O2 -L/usr/X11/lib  -o simple  simple.o libXw.a -lpng -lz  -lXext -lXmu -lXt -lX11 

/usr/lib/gcc-lib/i486-slackware-linux/3.3.6/../../../libpng.so: undefined reference to `pow' 

collect2: ld returned 1 exit status

also, I tried compiling xmoto recently and here's the ./configure result:

Code:

checking for jpeg_CreateCompress in -ljpeg... yes 

checking for png_read_image in -lpng... no 

libpng required!

...
I have libpng installed, symbolic links created (although maybe not all that are necessary).
I've read here that I should do the following:

1) modify ./configure of libpng - current version of libpng doesn't come with a valid config file
2) install libpng-devel - done that and didn't help

Thank you for eventual replies