Copying png images from source to build directory?

[C Y]

Can anyone help me with what I'm hoping is a fairly straightforward problem:

I need to copy png files from a source directory location to an 
out-of-directory build location, e.g.

src/images/image.png

to 

build/images/image.png

but can't figure out how to create a make rule to do this.  The background is 
I'm doing docbook building and need the images to be in the location expected 
by the docbook files to generate pdf output - obviously it works 
in-source-directory building but not out of dir.

So far, all my attempts to write a make rule that simply copies the images from 
source directory to build directory have failed.  I am currently hacking around 
it by naming all my images with a .docpng prefix and defining a build rule, but 
this is not really acceptable from a scaling standpoint as large numbers of 
images may need to be added, edited and maintained in the future.

Can anybody suggest a good solid way to do this with make? 

Thanks,
CY