I added my featured image. Now the image displayed on my blog posts are technically around 768px wide I think, so putting the 2048px image there is not very efficient. If I resize all images to 768px and open the website on the newest iPad in landscape mode, the image looks way pixelated. It looks good on my phone and computer though.
Is it possible to automatically show an attachment version of this image(Large) which is 768px to the user?
Is it possible to show 2048px image version for high resolution (retina etc) displays?
How are these things usually handled by WordPress? Do I have to custom code something or are there plugins to solve these problems?
I have the same problem with images inside the post basically.
WordPress uses SRCSET for handing image sizes. So if you upload a 2048px image this is saved, it then creates the Large, Medium and Thumbnail sizes. The site will then display the most appropriate sized images for its needs.
You can change the media sizes in Settings > Media to suit your needs. This will then apply to any images you upload. Any existing images on the site will need to be regenerated, using a plugin like this: