since it apeared in my twitter few days ago.
Pure bullshit ! Sorry folks. Image should be used for "Content"
and ALT should really represent content, so it SHOULD describe what is on the image.
For "trick" like heart image, button image etc...
we are talking about
alternate graphical representation for text
not alternate text representation of graphical image content.
So it is all wrong from the begining
from the very markup point of view.
Use any reasonable tag to encapsulate text and style it using CSS.
It can be ABBR if you text contains shortened form like heart pictogram,
or use A HREF if you want to link as well, STRONG,
or use SPAN in the worst case.
save the document by pressing <img alt="save button">
save the document by pressing <span class="img-as-text save-btn">save button</span>.
heart example would look like: