title: PNG or JPEG With Custom Text Chunk
body: <p>I normally like to ask much more precise questions but in this one I haven't found any good place to get started.</p>
  
  <p>Writing in C#, I am trying to add a large custom text chunk to an image and save this using either JPEG or PNG. I have found plenty of examples on using the Comments or UserComments tag and they work when the text is relatively short. In my case I need to add potentially large chunks of text, let's say up to 256K. I have found references to "custom chunks" but I can't find any good pointers on how to write and read them from C# without having to write a complete custom JPG or PNG encoder.</p>