@jon j,
Png's or jpg's have the width and height in their respective headers. More or less a col/row values to loop over the rgb(a) values stored into the files. There is no information about orientation.
When the site php reads them it uses them to generate the embed. In html IMG natural size is then used to define the display size in ratio..
If I open your picture, its having the orientation defined into the pixels layout. So you have probably made the pict using your phone in vertical position. As phone generate rectangular lpicts, Some phones check the orientation before they encode the cam info into raw files and invert the values. Vertical would then have an height greater than width and vice versa. Some do not.
Because the devices must respect the artist, an upside down or 30 deg rotation is kept as is.
Short story, to correct, inspect your picts on your device before upload, resize, rotate or crop (not every picts deserves a 6k x 8k pixel info) 1024 to 2048 is more than enough for this forum.