WiscWeb - Auto Scaling of images with "-scaled" file name
In version 5.3, WordPress rolled out a change to the behavior of the Media Library such that images larger than a certain size will be automatically scaled upon upload. WordPress can now detect when an image exceeds the maximum recommended web-optimized size and will scale the file down and append "-scaled" to the file name.
More information on this change can be found on the WordPress.org website.
Auto-scaling of images can result in lower image resolutions.
It will also rename your file name by appending "-scaled" before the file extension. (Example: filename-scaled.jpg)
The best way to avoid auto-scaling is to resize your image outside of WordPress, prior to uploading it to the Media Library. It is recommended that a user use a program like Photoshop to accomplish this. This can also help with appropriately sizing images to the page elements you're planning to use them in.