How can I convert image url to system.drawing.image

You could use WebClient class to download image and then MemoryStream to read it:

C#

WebClient wc = new WebClient();
byte[] bytes = wc.DownloadData("http://localhost/image.gif");
MemoryStream ms = new MemoryStream(bytes);
System.Drawing.Image img = System.Drawing.Image.FromStream(ms);

VB

Dim wc As New WebClient()
Dim bytes As Byte() = wc.DownloadData("http://localhost/image.gif")
Dim ms As New MemoryStream(bytes)
Dim img As System.Drawing.Image = System.Drawing.Image.FromStream(ms)

You can use HttpClient and accomplish this task async with few lines of code.

public async Task<Bitmap> GetImageFromUrl(string url)
    {
        var httpClient = new HttpClient();
        var stream = await httpClient.GetStreamAsync(url);
        return new Bitmap(stream);
    }

The other answers are also correct, but it hurts to see the Webclient and MemoryStream not getting disposed, I recommend putting your code in a using.

Example code:

using (var wc = new WebClient())
{
    using (var imgStream = new MemoryStream(wc.DownloadData(imgUrl)))
    {
        using (var objImage = Image.FromStream(imgStream))
        {
            //do stuff with the image
        }
    }
}

The required imports at top of your file are System.IO, System.Net & System.Drawing

In VB.net the syntax was using wc as WebClient = new WebClient() { etc