I needed to check to see if a URL that the user was entering was a valid Url, does it contain HTTP:// or HTTPS:// I ended up writing a small ValidationAttribute to add to the collection I am now building up, here is the code:

using System;
using System.ComponentModel.DataAnnotations;
using System.Net;

public class IsUriAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        var myString = value.ToString();
        Uri myUri;
        if (Uri.TryCreate(myString, UriKind.Absolute, out myUri) && (myUri.Scheme == Uri.UriSchemeHttp || myUri.Scheme == Uri.UriSchemeHttps))
        {
            return ValidateUri(myUri);
        }
        return new ValidationResult("URL is invalid.\nStart with http:// or https:// and end with\na proper image extension");
    }

    private ValidationResult ValidateUri(Uri myUri)
    {
        var webRequest = WebRequest.Create(myUri);
        try
        {
            webRequest.GetResponse();
        }
        catch //If exception thrown then couldn't get response from address
        {
            return new ValidationResult("URL is invalid and does not exist");
        }
        return ValidationResult.Success;
    }
}