With the native build-in lazy-loading for images in browsers, hinders the Web Clipper browser addon from capturing high-res rendered images, unless the image is already loaded in the browser viewport. A workaround for this is by scrolling down to the end of the page and it will load all the images to its proper resolution, instead of capturing the low-res placeholder images.
Joplin for Desktop
Joplin 1.2.6 (prod, win32)
Revision: f5f117cb (master)
Win 10 64x