Jonathan Desrosiers

In WordPress 5.3, several improvements were made to how images are processed. One of these improvements was the concept of “BIG images”. When an image is uploaded that exceeds the “BIG image” threshold (2560 by default), a new “full” size image is generated. This new image is then used instead of the true original when generating image subsizes to reduce server load.
Prior to 5.3, it was possible for the originally uploaded image to be displayed on the front-end, even when they were not “web ready”. Unnecessarily large images can be bad for performance and wastes bandwidth (which is unfortunate for those with slow Internet, or bandwidth caps by their service plans). This new full size image will now be displayed instead.
There are some scenarios where disabling this threshold would be desired, though. Maybe you run a photography site that 
needs to display original images, or your theme has full screen backgrounds.
This plugin disables the “BIG” image threshold and preserves the true originally uploaded image as the full size.
For more information on the improvements to image processing in WordPress 5.3, check out these <a href="https://make.wordpress.org/core/2019/10/09/introducing-handling-of-big-images-in-wordpress-5-3/" rel="nofollow ugc">developer</a> <a href="https://make.wordpress.org/core/2019/10/11/updates-to-image-processing-in-wordpress-5-3/" rel="nofollow ugc">notes</a> on the <a href="https://make.wordpress.org/core/" rel="nofollow ugc">Making WordPress Core blog</a>.

Disable "BIG Image" Threshold

Disables the "BIG image" threshold introduced in WordPress 5.3.

Urgor

Show big (original) images from blogs post page. It get all link hrefs with image anchors (like <a href="some_big_image.jpg" rel="nofollow ugc"></a>) and then leafs through with big images in full screen. It allows simple key (left, right, esc) and mouse navigating.

Big image browser

Full screen view of images that is in topic page. Keys navigated.

Disable "BIG Image" Threshold vs Big image browser