How many PIXELS by PIXELS for a posted image

 Hi Everybody,
  I have yet to figure out what size  in PIXELS by PIXELS should be used for posting an image or photo.
  I have yet to figure out what this forum or its predecessor did with PIXELS by PIXELS  for an image.
It's obviously being zoomed or rather resampled as the zoom level changes but what's the logic behind it.

I am not concerned about the file size in bytes.  JPEG is an incredibly rugged format.  A 512 Kb byte size for a JPEG on an average monitor is overkill even for a photo of trees.  Most digital cameras deliver JPEGs which have been compressed by about ten to one in byte size.  It hasn't been an issue for the last ten years.

However, the size in PIXELS by PIXELS is critical to resolution.  Newsgroups posted photos at "actual" size.  Thus I knew that my posted photos should be 980 x 700 PIXELS by PIXELS in order to keep everything on one page for most viewers.

So what happens to the PIXELS by PIXELS size when I post a 980 x 700 PIXELS by PIXELS photo in this forum.
Phil