Image to byte array from a url

WebClient.DownloadData is the easiest way.

string someUrl = "http://www.google.com/images/logos/ps_logo2.png"; 
using (var webClient = new WebClient()) { 
    byte[] imageBytes = webClient.DownloadData(someUrl);
}

If you need an asynchronous version:

using (var client = new HttpClient())
{
    using (var response = await client.GetAsync(url))
    {
        byte[] imageBytes =
            await response.Content.ReadAsByteArrayAsync().ConfigureAwait(false);
    }
}