Hey photo editing programs — I’m looking at you, Photoshop — a lot of you allow people to place text into graphic images, usually as a text layer. Most graphics with text on the web are made this way. Then we export the image as a jpeg or png/gif, flatting the layers so our artful text is displayed. This is how all the buttons with words are made, as well as the title banner graphics on most web sites.
So photo editors, when you render and flatten the layers, take the visible text (you know what it is) and include it in a tag inside the file, such as the EXIF information. Possibly as the caption if there isn’t already one. Let us disable this, including on just a single layer, but providing it would be a good default.
Then all the web spiders/search engines would be able to find that text. Web page editors could offer that text as a possible “alt” text for the graphic. And the blind would be able to have their web-page readers read to them the text embedded in graphics.