Anyone can suggest images for inclusion in the Showcase Gallery http://www.geograph.org.uk/gallery.php just click the 'suggest images' link top right on any gallery page. Viewers can then 'rate' the images using the scale on the right.
You can also build your own collection of favourite images by using the 'thumbs up' on the photo page .
The community showcase http://www.geograph.org.uk/results/200 has been used to show pictures that have cropped up in site features other than their picture pages themselves. The source (or combination of sources) has been different at different times and is likely to change as new features are being developed. As an example, images shown in busy forum threads may end up in the community showcase.
Click the link 'Use of my photos around the site' near the foot of your profile page.
Follow the link at the top of the page you arrive at to get notification emails of new additions in selected areas.
The Photo of the Week competition is an informal competition intended to showcase some of the best images submitted during the week.
The only criterion for an image to be considered is that it must have been taken during the qualifying week, which runs from Saturday to Friday, and submitted by midnight on the following Tuesday.
Some people like to make sure that their images are submitted within the qualifying period, and other like to delay their submissions to make sure they are not considered.
What constitutes 'best' is very much subjective, because the selections of both shortlist and winner are done by different contributors each week.
As with all subjective selections, there is often disagreement with some of the selections, but that usually manifests itself by people saying which image they would have picked if it had been up to them to do so.
It all takes place in the Discussion Forum "Photograph of the Year (date)".