I am trying to make a simple photo gallery website. Using ASP.NET and C#. Right now I don\'t have a server set up but I am just using the development one that Visual Studio
You're creating an element with a URL of C:\Users\Jordan\Desktop\Web Images\SomeImage.jpg. Obviously, that won't work in a web browser.
You should copy the images to a subfolder of your project, and set the URL to a relative URL, like this:
img.ImageUrl = "~/Web Images/" + Path.GetFileName(s);
(Assuming that the Web Images folder is a subfolder of the application root)