Use an image
type input:
<input type="image" src="/Button1.jpg" border="0" alt="Submit" />
The full HTML:
<form id='formName' name='formName' onsubmit='redirect();return false;'>_x000D_
<div class="style7">_x000D_
<input type='text' id='userInput' name='userInput' value=''>_x000D_
<input type="image" name="submit" src="https://jekyllcodex.org/uploads/grumpycat.jpg" border="0" alt="Submit" style="width: 50px;" />_x000D_
</div>_x000D_
</form>
_x000D_