I'm pretty sure you want to add something like this...
<asp:imagebutton id="Image_ID" runat="server" postbackurl="secondpage.aspx?Img_ID=<%# DataBinder.Eval(Container.DataItem," imageid=") %>"imageurl"<%# DataBinder.Eval(Container.DataItem,"imagepath") %>" xmlns:asp="#unknown" />
I replaced the double quotes around the postbackurl with single quotes to fix the problem of improper nesting. If that doesn't work, create an onbind event handler for the datalist and set the onclick event for the button there.