using System.Windows.Forms;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;

private void TransImageToClipboard(Image img)
{
using (var stream = new MemoryStream())
{
img.Save(stream, ImageFormat.Png);
var data = new DataObject("PNG", stream);

Clipboard.Clear();
Clipboard.SetDataObject(data, true);
}
}