If one opens the VE editing interface, the user experience in relation to image formats varies significantly. The report:
has several examples with different browsers like
FF 22 / Win 7: edgewise images smaller; rest bigger.
Chrome 28 / Win 7: all significantly smaller.
See also screenshots in perma link.
Version: unspecified
Severity: normal
When viewing a page, images that are specified as [[File:Foo.jpg|thumb|Caption]] render as 220px wide (en.wp)/180px wide (de.wp), regardless of dimensions or aspect ratio.
In visual editor, images specified the same way render so as not to exceed 190px wide by 212px high.
This means that images can appear at very different sizes in the VE editing surface to how they appear on the rendered page. This is especially true for very tall images.
Example to better illustrate this, compare the two views of this page
View mode: https://en.wikipedia.org/w/index.php?title=User:Thryduulf/sandbox4&oldid=575350620
VE edit mode: https://en.wikipedia.org/w/index.php?title=User:Thryduulf/sandbox4&oldid=575350620&veaction=edit