Blurry images on the site how to fix?

Question

Images

Good afternoon! on the site https://rentakm.ru/ in the slider on the main page called "Company News" the pictures are not clear and blurry. When viewing that from the phone that from the PC. The programmer throws up his hands, says there are no filters, the point is in the picture itself. I already uploaded a picture of different resolutions, it's useless. The same with pictures on the general news page.
This does not happen in other sections with pictures!
Because of what it can be?

Answer 1

Obviously, preview images are generated for your main page to save user traffic (good practice). Because of this, the images appear to be blurry. In general, I did not see a strong blur even on the retina. Yes, the pictures are not very high quality, but in this size, the details do not need to be considered.

Answer 2

Can this be turned off? With unlimited internet, it seems like everyone now has it .. But such pictures somehow don’t look very good