Home pages are the most valuable real estate in the world. Each year, companies and individuals funnel millions of dollars through a space that's not even a square foot in size.
Jakob Nielsen's Alertbox, May 12, 2002
One of the first problem one has to face publishing photos on the web is that the picture you are publishing is of rectangular (at most) shape. Web can be considered a recursive nesting of rectangular shapes. So the shape you are publishing will have to fight for its own attention among several others starting from the shape of the monitor.
I am speaking here of the diffused rectangular shape dating back to the old days of 35mm film. This shape transmigrated, almost untouched, in DX, FX and 4/3 digital formats.
I am using horizontal to mean a rectangular frame who's longest side is on the upper and lower side, vertical otherwise.
In landscape the horizontal frame is not a big problem till you get to something you want to insulate that is pretty vertical. The braindead rule here is that horizontal things go horizontal and vertical go accordingly. However this is not that useful at all. If you put something vertical in a vertical shape you will have two vertical vector competing for predominance.
Sometimes vertical can be carefull composed in a horizontal frame but it is not the norm.
To get things worse web is not vertical friendly. First the monitors tend to have an horizontal frame, and the omnipresent wide screen are even more pronounced in this shape.
Second typical web and browser formats are vertical like 800x600 or 1024x728.
If you chose to go vertical you will have to scale the image more than an horizontal one and you will have a pretty predominant set of horizontal vectors either from the monitor either from the browser.
Recently following and reviewing the web pictures of one of my preferred contemporary landscapist, Mark Hobson, i have appreciated his use of the square format. In web terms it is simply perfect. In compositional terms i not so sure for it's use everywhere. Certainly it is far better in vertical situations where the vertical of the composition can live in a better way.
Next i am going to publish some experiments.