Is there a reason you could not give the element an identifier?
i.e:.
<input id='myButton' type=image src="/lihtml/test_button3.gif" align=left alt=File_Certificate_Go>
then
document.getElementById('myButton').click()
edit: , , , :
var elms = document.getElementsByTagName("input");
for (var i=0; i< elms.length; i++)
if(elms[i].src = '/lihtml/test_button3.gif') { elms[i].click(); }
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