Here is how you can add text to all your photos on any device using the default applications available on them.

Use these free online tools to add text to images. You can add overlay text, add a simple text or customize it with fonts, colors, etc., ...

This article shows how to add transparent text to an image in Photoshop. The article also shows why smart images can be better.

Select this to add alt text to your photo. Twitter alt text has a 1,000-character limit, and you can consult the website's own advice for writing accessible picture description, as well.