... alt tags are used to tell google what exactly it is
No, alt text is used to tell human visitors what the image is, if they are unable to view it, for whatever reason. This could be because they are a blind visitor using assistive technology, somebody using a text-only browser or because the image has failed to download for some reason. Yes, the search engines can also read and make use of this text, but that is not its main purpose and it should not be written from that perspective.
ALT tag we use on images, we put our websites keywords as ALT tag on images so google can read and give value to the websites.. ALT tag very important in SEO and helpful to promote our websites in search engines.