Is this possible with PHP?

Before I spend hours attempting a configuration of PHP that will fail in its intended effect, I thought I'd search for some PHP guru wisdom. PHP has the following image function: imagefilter ( resource $image , int $filtertype [, int $arg1 [, int $arg2 [, int $arg3 [, int $arg4 ]]]] ); which can be used to control the opacity of a graphics file.

That function interest me because my hope is that it can accomplish the following.

My homepage uses the traditional three column format with boxes in the right and left columns. I have a background image which I believe is aesthetically compelling. Therefore, I've made transparent (about 30%) the boxes. The problem is that within the boxes are my product images which I don't want transparent. I want them to jump out at the viewer at 100% opacity. So far all my strategies to accomplish this have failed. The transparency of the boxes superceds that of its graphical content. My hope is that the above copied image function can overcome this limitation. Its use, however, will require some non-trivial PHP changes and time-consuming experimentation.

Therefore, there's the question. Is my goal unattainable?