I generally use Photoshop or Irfanview to resize images and I work in the number of pixels along the edge. When I resize an image of 4000 X 3000 pixels to 1000 X 750 pixels, the number of pixels is reduced from 12,000,000 to 750,000 or 1/16 of the original number. The image quality is not degraded to the point where it can be seen on most computer displays. The screen that I am looking at right now has a resolution of 1280 X 800 pixels, so a file with 1000 pixels on the long edge could be around 3/4 of the display size without degradation. The file size is considerably smaller even with .jpg, which is compressed anyway. The biggest problem with resizing images is the time and effort that it takes to do it. I would expect that there is batch software that can do this, but I usually like to crop and correct contrast and brightness before resizing. I don't think of image size in inches until I print one. This was true even with film. The grain on film was usually fine enough to allow considerable enlargement without noticeable loss of quality. Another advantage of resizing is that if someone steals your image, the quality will never be as good as your original. Image theft isn't a big deal for most people, but it can be.