: SEO impact of dynamically serving cropped images based on device type I have a website and try to optimize it regarding device size. Due to a large image slider on the front page I could

@Eichhorn148

The only SEO that might change by dynamically serving an appropriate sized image for the device would be the ranking of that image itself in Google image search.

Google is fine with serving different content to different devices as long as you treat Googlebot mobile user agents the same way that you would treat the corresponding mobile device. They have said that there is no ranking preference for responsive, vs user agent sniffing vs separate mobile site.

Using a "Vary: User Agent" HTTP header would be a good idea because proxies that cache your page wouldn't serve the wrong image to the wrong device for you.

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@BetL925

Before your question was clarified, you had said that you had a responsive site. Here is how you would use responsive CSS to change the image based on browser size:
@media screen and (max-width:480px) {
#myimage {
background:url('/smaller-image.png');
}
} @media screen and (min-width:481px) {
#myimage {
background:url('/bigger-image.png');
}
}


Using user agent sniffing is not actually considered to be responsive. User agent sniffing is a fine technique for creating a mobile site from Google's ranking perspective.

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