Alt text! ALWAYS alt text, because in the HTML page structure, it’s PART of the image element’s attributes.
If it’s not, it gets separated and, particularly with the way modern content management systems render text (often as weird separate chunks), can’t be easily found.
Putting “image id” text in front of a description is NOT standard accessibility practice. Using ALT text is supported by all browsers and screen reader software.
DO NOT duplicate alt text and visible text, because then a visually impaired user has to listen to it twice.
If you need visible captions paired with images, use the HTML figure and figcaption elements - you can use different alt text there to add information a visually impaired user needs, and the figcaption to explain the meaning for all audiences.
Also, learn to write helpful image descriptions! And generally, only write alt text for images that are informative, not decorative.