After recompiling php 4.2.3 with the gd image functions, I've found that libpng 1.2.5 is not compatible with php 4.2.3. While loading a png file using ImageCreateFromPNG($img); where $img is the filename, php would segfault. After recompiling php multiple times, i've still had the same problem. I gave the stable version of php in the development stage a try, and still recieved a segfault. So then i used the strace function at the command line along with the php cli to figure out that it would segfault when the png image was loaded. When i viewed the libpng website, i found the following...

"The current public release, libpng 1.2.5, has a new API (since 1.0.x) for dynamically enabling and disabling certain optimizations (currently limited to MMX code--which is compiled into GNU C versions only if PNG_THREAD_UNSAFE_OK is defined, due to the gcc code's use of static global variables to work around addressing limitations). As a consequence of this and some other changes, its DLL and shared-library (.so) numbers were bumped from 2 to 3."

After reading this, i've decided to downgrade to libpng1.0.15 and recompiled php. After doing this, the segfault would not appear again.

Hopes this helps...