Not sure if you're still experiencing this. I had same issue, but only with a few images out of the many on my board. Refreshing tab, restarting browser, copy/pasting image all had no effect.

My solution was:

1. Download the blurry image.
2. Reupload image (image appeared full quality)
3. Replace blurry image with clear image on board.

Obviously not perfect, but helped.

Thank you, @Lachlan Mackenzie for the tips! Much appreciated! 

Sorry to hear about the issues, @Irina Folkneresque. Here is an older thread that also features some tips on blurry images. I hope that this is helpful.

Hi @Irina Folkneresque - we also suggest following the below steps if you’re still seeing blurry images: 

The first step I would suggest taking is to reset the application data - steps can be found in this article:

https://help.miro.com/hc/en-us/articles/360017572854-Desktop-app

If that doesn't resolve your issue, please tell us more about your setup, e.g., OS and version, laptop or external monitor, screen resolution (with scaling applied?).