I frequent WetCanvas.com, and I cannot figure out how to post a photo in a thread. The usual way is to click the button to select a file from a list. I tried copying an image and pasting in the text box, but that just pastes the file name and the image doesn’t appear.
— Shirl
Yes, clicking a button to upload a file won't work on the iPad because there is no (accessible) file system. So you can't do it, at least not in Safari. Some apps, like WordPress, allow you to do this. But of course that would mean WeCanvas would need to provide a custom app.