I was wondering why the thumbnails of my website look blurry on mobile. I tried uploading a bigger size or resolution but it keeps happening. It looks fine on desktop and then it seems grainy and blurry when on mobile. I uploaded a 170x170 image. There's an image of the area affected attached, it looks sharp taken from the computer, but checking that same area on the phone you will see it blurry.
Please let me know what's the best way to avoid this, thank you.