When you put in your image to the "Drop Image Here" prompt, you will then select "Unconditional" if the image is clear. (sometimes "Conditional" is used when the image isn't easily described or is blurry or unintelligible.) Then, press "Submit" and watch the magic happen. It will give you the caption of the image and then also the HTML code for the alt tag. This is all done by using databases such as GPT API, Gradio, and many python libraries.

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An "Alt Tag" is a caption describing an image so that a screen reader can read it and speak the image to whatever person needs such device. Although this is mandated at the least for Web Accessibility, you will rarely see them, let alone descriptive ones.