function showImage(imageFileName, Make, Model)
See that? The function wants you to pass it *THREE* (3) arguments.
But when you call it here
cho "<td align=center><input type='button' value='showImage' onClick='showImage(\"$cameras\");'></td>";
you are clearly passing only *ONE* (1) argument to the function.
What a surprise that you can't use Make and Model in the function.