Choose a resolution and compression level suited to the displayed size, and specify image width and height. Images outside the initial viewport can load lazily, but avoid lazy-loading the main initial image, especially the LCP image. Measure the actual loading effect of each change.
Alt text should explain an image in context without keyword stuffing. Current major browsers support WebP and AVIF. Compare quality, file size, and audience compatibility, providing fallback formats with picture when needed. A format conversion alone does not guarantee search visibility or better LCP.