Testing high PPI vs high resolution images for the web

A test to see if there is a difference between increasing PPI vs increasing resolution for images on the web.

photo of flowers in a variety of colours
Type: 400px JPEG photo at 72ppi
Size: 78 KB
photo of flowers in a variety of colours
Type: 400px JPEG photo at 144ppi
Size: 78 KB
photo of flowers in a variety of colours
Type: 400px JPEG photo at 216ppi
Size: 74 KB
photo of flowers in a variety of colours
Type: 400px JPEG photo @2x (800px)
Size: 164 KB
photo of flowers in a variety of colours
Type: 400px JPEG photo @3x (1200px)
Size: 307 KB
image with shapes and letters
Type: 400px PNG image at 72ppi
Size: 12 KB
image with shapes and letters
Type: 400px PNG image at 144ppi
Size: 12 KB
image with shapes and letters
Type: 400px PNG image at 216ppi
Size: 12 KB
image with shapes and letters
Type: 400px PNG image @2x (800px)
Size: 20 KB
image with shapes and letters
Type: 400px PNG image @3x (1200px)
Size: 33 KB