Merge transparent PNG images using PHP

I'm looking for a capable developer who can create a PHP script (with AJAX features) to merge multiple transparent 24-bit PNG image files. With merging I mean actually combining the images as layers on top of each other, and not adding the next to each other. This can (for example) be achieved using the PHP imagecopymerge() function. All PNG files that will be merged are transparent, and should stay transparent. This script will be used privately, so don't worry about adding any design to it. I am only looking for functionality. It should work as follows (but feel free to improve on it): The script should look into multiple subfolders e.g.: /images/background/trees/*.png /images/background/ocean/*.png /images/sky/stars/*.png /images/sky/clouds/*.png /images/sky/planes/boeing/*.png /images/sky/planes/airbus/*.png /images/buildings/offices/*.png etc. It should then show a dropdown box to the script page, where the user can select a directory/folder. The dropdown box will initially show all first level folders e.g.: /background /sky /buildings After selecting a 1st level folder, then the user should select the subfolder(s): e.g. if /background was selected, it will present: /trees /ocean When the script detects a PNG image, it should present the name in the dropdown list. When selecting the image name, it should also show a thumbnail sample of the image (with option to click on it to open in a new window) right away on the right (using AJAX). Please note that images will never be found in folders that contain folder. The images are always present at the ending subdirectory. Now the script should allow the user to merge it with another image, by showing a link "Add another image" which will present another dropdown selection box. The user should be able to do this up to 25 times (so merge a maximum of 25 images together). After the user adds the second image (and third, and fourth and so on) the script should automatically present the merged image at the bottom of the page. So the merged image should change in real time using AJAX. As this may take a while, feel free to add a loading message during this time. The script should also have the option to remove or edit an image from the merge (by showing a 'delete' or 'edit' icon next to a dropdown box), and thus create a new example at the bottom of the screen with the new or remaining images to be merged (if there are more than 1 selections). The first selected image is always merged as the bottom layer. So for example, 'backgrounds' would be selected first, the second image will be merged on top of that, the third will be merged on top of those two etc. etc. While not all images in the directories have the same dimension, all images that will be merged will have the exact same dimensions. Images that are in the same directory will NEVER be merged, so you don't have to add this to the script. This should be a rather easy and straightforward script for an experienced developer. I look forward to any bids.