About those Test Posts about 4 posts below...

When inserting pictures into these blogs you get a choice for sizes.  A year ago when I started I used Large, now I use Extra Large.  There are also Small and Medium options illustrated below.
There is also the option to use "Original Size".  I use it occasionally for slightly oversize images, but I wanted to see how it would work for really big images.   Thus the test posts, one for "Landscape" (wide) and "Portrait" (tall).
They are in the middle of today's posts because I want them below the end of the Archive list on the right.
The sizes are in pixels, width first.  So a landscape 900x600 is 900 pixels wide and 600 pixels tall.
What I found is the portrait oriented images max out at a little over 1000 pixels wide, so a 1200x1800 looks a little wider than a 1000x1500, but looks exactly the same as a 1600x2400.
On the other hand the landscape oriented (wide) images max out a little over 1500 pixels wide, so an 1800x1200 looks a little wider than a 1500x1000, but looks exactly the same as a 2400x1600.
Interesting.  If I want to post a picture that will look as wide as possible, it will either be a portrait 1100x1650, which will look 1100 pixels wide, or a landscape 1650x1100, which will look 1650 pixels wide.
Small:                                                                                                                                        Medium: