Virtue theme image quality loss

Hello,

I have problem with image quality at the main site of Virtue theme. I don’t know why but the minatures of images are in very low quality, even their quality is not in fact bad.

I was searching for help in this forum, but even I’ve read some opinins, none were helpful, such as installing WP Resized Image Quality plugin.

the site is:

Please help, I wish my blog looked proffessional and I have no idea what can help.

Best Regards,
Karolina