Here is an easy way to output an image tag from an image field with possibility to use some new enhancements

Sitecore.Xml.Xsl.XslHelper xslhelper = new Sitecore.Xml.Xsl.XslHelper();

string output = xslhelper.image("ImageField", Factory.CreateItemNavigator(Sitecore.Context.Item).Select("."));

Response.Write(output);