one cannot display on wikipedia a thumbnail of File:George-W-Bush.jpeg
at a height of exactly 600px. one can attempt to constrain it by height
and no width (enter [[File:George-W-Bush.jpeg|x600px]]).
however this produces a 453 × 599 image (!) while the next available size
454 × 601.
suppose a user needs to arrange horizontally several photos of arbitrary
dimension while keeping their top and bottom edges aligned. in many cases
this requires working backwards by coin-shaving the original images in a
graphics editor until round( $srcHeight * $dstWidth / $srcWidth ) happens
to equal the desired height.
for narrower aspect ratios (flag-poles, longcat, yao ming) this issue will
be more certain to arise.
the most obvious solution is to pass the size parameter directly to image-
magick as widthlessly (breadthlessly?) specified, e.g. this serves me well
for a local copy of the same photograph; the height is not replaced by a
dependent round-trip calculation.
owner@lappy:~$ convert George-W-Bush.jpeg -thumbnail x600 w.jpg
owner@lappy:~$ identify w.jpg
w.jpg JPEG 453x600 453x600+0+0 8-bit DirectClass 86.2KiB 0.000u 0:00.000
since mediawiki isn't doing it this way already, i should guess the real
issue lies in gracefully adopting a new thumbnail url pattern (one which incorporates the height-dimension in some fashion), or no?