Submitting web form from VB code

I am currently using the following to submit a web form:

element.click

where element has been found by :

For Each Element In Doc.All
If Element.tagName = "INPUT" Then
If Element.type = "text" Then
.
.
ElseIf Element.type = "submit" Then
.
Element.Click

This works fine for the majority of web forms but is unworkable
if the form uses some other method for submitting the form such as a custom image to be clicked.
Does anyone have any ideas as to how to find such an image in the page??