Hi, you dont have to use the gallery if you do not want to. You may upload your photo to anywhere on the web that you like. After you upload your photo somehwhere on the web you than click on the add picture button while you are making a post, enter in the url to the picture and you are all set.
If the upload failed did it give you an error message? I believe there is a 2mb file upload limit was you picture larger than that? Also make sure you choose a category to upload the photo to, I have seen it fail before because of that.
you just have to host it (i use imageshack, i know some people use photobucket), and then when you're posting you click on the button that says "insert image" when you hold your mouse over it, and you past the URL of your hosted image in the box that comes up. It doesn't have to be in the gallery first.