An image title, most often the filename itself (white-sports-car.jpg rather than IMG_4821.jpg), is a plain-language description that helps search engines understand what an image shows before they've even rendered it. "White sports car" describes the file more usefully than "car," and both describe it more usefully than a camera's auto-generated filename.
The goal is accurate description, not keyword density. Cramming a filename with every related term a page targets, white-sports-car-luxury-vehicle-sports-car-for-sale.jpg, reads as spam to search engines the same way keyword-stuffed body text does, and it doesn't actually help the image rank better than a clean, accurate name would. A good image filename or title tag describes what a person would actually see if they looked at the picture, ideally including the one or two words that genuinely matter, and stops there. Alt text does the heavier descriptive lifting; the filename just needs to be clean, specific, and not auto-generated gibberish.
