[HTML Techniques] Text alternatives for submit buttons [HTML Tests] 
All input elements with a type attribute value of "image" have an alt attribute. Alt text for all input elements with a type attribute value of "image" identifies the purpose or function of the image. Alt text for all input elements with a type attribute value of "image" does not use the words "submit" or "button" (English). Alt text for all input elements with a type attribute value of "image" contains all non decorative text in the image.