Image size problem

WD9 Premium (had the same problem on WD8)
I place an image on one of my web site pages, size 1200 x 851 px, OK this is larger than I need,
so I reduce the size, to fit say a third of my page, when I view the page on the Internet
the lover portion of the image is lost, say around 20%, so I have to reduce the size of my image,
maybe 2 or 3 times before all of the image is shown on my web page, the final size being W 514.2px H 365.3px.
The whole image I would like is shown when I preview the page but not when I upload?.

Post your .web file AND the url so we can see what you are seeing please, otherwise it's all guesswork.