These are several different attempts at reducing the picture size, just to see what works or doesn't.... (Sorry if the page takes a long time to load!)\ You can scroll down to each post on this one page, or click on these links, and each post will open in a separate browser page.
There's actually only 5 unique image files here, and all are in the "1.Original.... " post. (Three at 1647x815 and two at 824x457.) All others use the same exact files, but the size reduction is done by Google and/or your browser. Some browsers will automatically shrink or enlarge images AGAIN to fit the browser window, confusing things even further. With any image that has fine details, using the larger image and letting the browser reduce it yields unpredictable results, and also makes the page load much more slowly. 
testpages >
testpics
4. Google Resized to "Medium" (200x111) and "Small" (96x53)
Below are the original five (AE) but but Google is automatically resizing all of them to "Medium" = 200x111.
A. Below is the original fullsize pic
A. Above is the original fullsize picB. Below is a highercontrast version of the original
B. Above is a highercontrast version of the original
C. Below is a posterized version of the original
D. Below is a smoothedhalfsize of the highercontrast pic
E. Below is a highcontrast smoothedhalfsize of original
 Below are the original five, but but Google is automatically resizing all of them to "Small" = 96x53.
A. Below is the original fullsize pic
A. Above is the original fullsize picB. Below is a highercontrast version of the original
B. Above is a highercontrast version of the original
C. Below is a posterized version of the original
D. Below is a smoothedhalfsize of the highercontrast pic
E. Below is a highcontrast smoothedhalfsize of original

3. Google resized the original Five to "Large" (420x233)
Below are all five (A  E) repeated, but Google is automatically resizing all of them to "Large" = 420x233. A. Below is the original fullsize pic
A. Above is the original fullsize picB. Below is a highercontrast version of the original
B. Above is a highercontrast version of the original
C. Below is a posterized version of the original
D. Below is a smoothedhalfsize of the highercontrast pic
E. Below is a highcontrast smoothedhalfsize of original

2. 50% Google resize of the Original Five: (1647x915 > 824x458 >412x229)
Below are all five (A  E) repeated, but Google is resizing all of them by 50%
A. Below is the original fullsize pic
A. Above is the original fullsize picB. Below is a highercontrast version of the original
B. Above is a highercontrast version of the original
C. Below is a posterized version of the original
D. Below is a smoothedhalfsize of the highercontrast pic
E. Below is a highcontrast smoothedhalfsize of original

1. Original (1647x915), plus two fullsize and two halfsize alternates.
A. Below is the original 1647x915 jpg
A. Above is the original 1647x915 jpg
B. Below is a highercontrast version of the original
B. Above is a highercontrast version of the original
C. Below is a posterized version of the original
D. Below is a smoothedhalfsize of the highercontrast pic
E. Below is a highcontrast smoothedhalfsize of original

14 of 4