Do you mean you want to upload the images from the page up to your server?
You can use <asp:FileUpload> control + <asp:Button>
There are plenty of examples how to do it:
Code:
if (FileUpload1.HasFile) {
string fileName = Server.HtmlEncode(FileUpload1.FileName);
string extension = System.IO.Path.GetExtension(fileName);
if ((extension == ".jpg" )|| (extension == ".png"))
FileUpload1.SaveAs(MapPath("~/Uploads/" + FileUpload1.FileName));
}
Checking the file size is tricky: as of now, I think, you cannot use HTML5 File API (
http://dev.w3.org/2006/webapi/FileAPI/) and it means you cannot find out the file size before you upload the file to your server.
However, the common solution is to limit the request size in <httpRuntime maxRequestLength="2048" /> (2Mb)
If the uploaded file is bigger than the allowed request - ASP.NET will reject it (but you will have to handle the error)