[cannot post code in comments...]
To include the image in DocumentText, you can encode it into Base64
For example :
var img = System.Windows.Forms.Clipboard.GetImage();
if (img != null)
{
string sTempPath = System.IO.Path.GetTempPath();
sTempPath = String.Concat(sTempPath, "ClipTemp.jpg");
img.Save(sTempPath, System.Drawing.Imaging.ImageFormat.Jpeg);
string sStringBase64 = null;
using (var fs = new System.IO.FileStream(sTempPath, System.IO.FileMode.Open, System.IO.FileAccess.Read))
{
var sBuffer = new byte[fs.Length];
fs.Read(sBuffer, 0, (int)fs.Length);
sStringBase64 = Convert.ToBase64String(sBuffer);
}
var sDocumentText = String.Format(@"<html>
<body>
<img src=""data:image/jpg;base64,{0}""/>
</body>
</html>", sStringBase64);
webBrowser1.DocumentText = sDocumentText;
}