Low definition mobile images

Hello! I’ve noticed that some thumbnails on my website are having low definition on phones. This does not happen on PCs or in big images on mobiles. Only on small/medium sized images on my mobile home page. Does someone knows what’s going on? I kindly appreciate all your responses. Thank you!

Ewerton

Here’s my website: http://scibreak.com.br/

Hi

You can try a plugin like WP Retina 2x to increase the image quality. The plugin can be found here: https://wordpress.org/plugins/wp-retina-2x/

Thanks!