From article Sample code you can add more line of code to save the Base64 value in hiddenField and on code behind pass it as byte value and save it to DataBase.
Add One Hidden Field to store Base64 value.
<asp:HiddenField ID="ImageVal" runat="server" />
Add the line of code below to your this line to store the Base64 value in HiddenField.
$("#imgCapture").attr("src", base64);
Set The Hidden field Value as per Base64 value.
$('[Id*=ImageVal]').val(base64);
Pass this value to your Database Call method for saving byte Type Data to Image dataType column.
byte[] bytes = Convert.FromBase64String(ImageVal.Value.Split(',')[1]);
Just refer the below sample code how to work with database in SQL and you can implement it by your code logic as there only saving the path in database you can add image or byte datatype and pass the Byte data on saving.
https://www.aspforums.net/Threads/183525/Save-digital-signature-in-Database-and-display-in-ASPNet-GridView-using-C-and-VBNet/Replies/6#Replie