Most of my images are published in a format that is 640 pixels across the image with a depth of 72 pixels. These are drawn from hi-res RAW photographs with far higher resolution (eg 4,000+ pixels across with a depth of 300+ pixels).
In some case - like the below picture - the picture is a composite of many individual photographs, stitched together to form a single picture.
Sometimes, the big picture doesn't work out when it is, in turn, shrunk for web publication - it might have too much detail, or the shrinking/display process may introduce artifacts or blur not present in the original.
This picture was produced for a 10m by 15m wall - the summary photo here gives an idea of what the picture contains, but misses the detail. An extract of the detail is produced below.