To check if an image has alt text, try selecting the image with your screen reader on. or manually "Inspect" the image in any browser.

Adding alt text makes images accessible to users with visual impairments, low sight, dyslexia and other disabilities. When a screen reader comes across an image, it reads the alt text aloud. Users ...

Alt text makes images more accessible to blind users and others who use screen reader software. Anyone can add alt text to images, but it’s currently not required.