How can I compare the quality of two images?
Try WinMerge which is a free software to compare files and images and check differences between them. You can compare not two but three images at once using this great free software. It shows and highlights the differences between the images. If you want, you can also use a free online tool to compare two images.
What app can i use to compare two pictures?
VES - Image and Photo Compare
Then this is the app for you. With this app you can compare two pictures in different ways to find out which one is better. Through the various comparison options, you can quickly and easily determine even minor differences in the pictures.