problem with installing gtk.

[guru prasad <gphere4u gmail com>]

Hello,
I am newbie so please excuse me if i am asking childish thing. So now
the point is i have already working GTK  of version 1.2 something. So
now i tried to upgrade it by installing gtk 2.20.0. So i followed
needed procedures.
Installed latest pkg-config, lib png 1.4.x, freetype, fontconfig,
glib, pango atk,

laterward tried cairo 1.8.8, while configuring i faced following problem

/opt/newgtk/  is my directory for new gtk  tried to keep separate from
older version
linux:/opt/newgtk/cairo-1.8.8 # ./configure --prefix=/opt/newgtk/
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.
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checking for cairo's PNG functions feature...
configure: WARNING: Could not find libpng in the pkg-config search path
checking whether cairo's PNG functions feature could be enabled... no
configure: error: recommended PNG functions feature could not be enabled


But i have already installed linpng then also why i am facing this problem dono

i have libpng 1.4.X but my cairo is 1.8.8  Is there any version
incompatibility is there between these?

So can a kind soul tell me what my problem is?

Thanks & Regards,
Guruprasad.