Answer 1

Just add a preloader, and remove after loading of the entire page
https://code.sololearn.com/WneTMVOg34ne/?ref=app

or add srcset attribute for different type of device

<picture>
<source media="(max-width:320px)" srcset="low-quality image.ext" />
<source media ....... />
<img src="main-image.ext" />
</picture>

that will automatically load preferred quality for that particular device res.