dpreview.com challenges are online photo competitions defined by, open to and judged by members of the dpreview community.

Themes, rules and entrant limits are set by hosts, who can (or at least should) disqualify entries which don't meet a challenge's criteria. Any member of the dpreview community may apply to become a challenge host.

Any dpreview user can take part in the judging process for any challenge by rating images during that challenge's voting phase (entrants may not judge their own entries). Judging images is ultimately a subjective process and the challenge judging system reflects this. However, to address the most frequently asked questions we offer the following:

How does the ranking process work?

It's natural that people want to know how their input contributes towards each image's final ranking. Early in the design phase of the challenges system it was clear to us that simple techniques (counts, averages etc.) could not possibly handle the multitude of variables in our challenges (arbitrary number of votes, arbitrary number of users, subjective criteria, arbitrary number of images). Therefore the ranking algorithm we finally settled upon utilizes bayesian techniques instead.

A very rough paraphrasing of our actual ranking algorithm would be:

"each image's final rank is a combination of its average rating and our confidence in that average based on the number of people who rated it, compared to its peers"

Clear as mud? Well, don't worry, the beauty of the system is that one need not (and in fact should not) consider ranking mechanics when rating images. Just follow the judging guide below and have fun.

Judging: some rules of thumb

Excellent image that exemplifies theme Poor image that doesn't fit theme

1. Rate each image according to your own interpretation of:

   • how aesthetically pleasing is the image? AND
   • how well does the image meet (your interpretation of) the challenge's criteria (name, description & rules)

2. Rate high if images satisfy point #1, rate low if they don't
   Don't be afraid to award low ratings to images which don't make the cut. Entrants want genuine feedback and everybody knows we're not playing for sheep stations here. Don't forget that there are 'half' stars (0.5, 1.5 etc)

3. Judge each image on its own merits
   The final ranking system assumes that not all people will judge (or necessarily even see) every image. As images are shuffled during judging (to ensure equal exposure), better images will still receive more high-value ratings, pushing them to the top in the final ranking.

4. Every rating affects an image's final rank
   You cannot actively give a 'neutral' rating (what would be the point?). The closest you can come to that is not expressing an opinion at all - and you don't even need an internet connection to do that.

5. Rate as many, or as few, images as you wish
   We chose a rating system over a ranking system because it frees you (the judges) from having to judge every image. Voting on only a subset of images in a challenge has no negative impact on the fairness of final result so take it easy.