C# ASHX image handler for png's that are created runtime

Hi, I am currently working on a feature that allows a user to print a screenshot from my web application. The screenshot and application side of the feature is already done and I have already had a web developer work on parts of this and all work so far will be supplied. I have a web application that sends a png as a byte stream or a base64 encoded string in chunks to a javascript. After everything is received a popup is opened where the png is to be shown through a ashx file. The problem is that it is not displayed correctly or at all in all browsers. The feature must work in all major browsers, IE 7/8/9, Firefox, safari and chrome. So far It only works in IE 7 and partially in chrome. Most of the code is in C# and a little bit of html/javascript. There is approximately 130-170 lines of code across 4-5 files.