Each of the three ZIP files have...
- Affinity Photo: 2400 pixels wide, no compression (set to 100%), bilinear resample
- Shortpixel: 2400 pixels wide, Lossy compression
- Imagify: 2400 pixels wide, Ultra compression
- WP Compress: 2400 pixels wide, Ultra compression
All four images in each ZIP file were resized from their original image taken on a Nikon D-90 (each ~4200 pixels wide and > 6MB)