The 2011 World Press Photo is now open for entries. Photographers are invited to enter in 18 categories - Spot News, General News, People in the News, Sports, Contemporary Issues, Daily, Portraits, Arts and Entertainment and Nature - each of which can be entered with single images or portfolios. Portfolios are limited to 12 images.

All images submitted must have been shot in 2010. They must be at least 3000 pixels in length, have an embedded ICC profile and can't be submitted in CMYK mode.

World Press Photo also points out that the content of the images must not have been altered. "Only retouching which conforms to currently accepted standards in the industry is allowed. The jury is the ultimate arbiter of these standards and may at its discretion request the original, unretouched file as recorded by the camera or an untoned scan of the negative or slide."

Earlier this year, one photographer, Stepan Rudik, was disqualified. He was the winner of the 3rd prize story in Sports Features, but lost his title "due to violation of the rules of the World Press Photo Contest."

Speaking to BJP, a spokeswoman for World Press Photo said that the photographer had removed the foot of one its subjects from a photo. However, Rudik, in an interview with BJP, said that he was within his right to crop and submit a black-and-white photo despite shooting it in colour.

"In my opinion, the so called 'objectivity' ends where the picture frame starts," Rudik told BJP. "And black and white photography itself - is it objective? Has anybody seen the black and white world? A photographer chooses at the time of photographing to take a bit to the left or a bit to the right. I find the comments that one should not crop the already shot frame ridiculous. It is my right as the author to crop from the shot frame as I think proper in order to highlight the detail I need for creating the series. In my case, I think that what I did can be equated to retouching, as if it were a defect of a film." Read our full interview here.

For this year's contest, photographers have until 13 January 2011 to submit their images. However, the must request a username and password to the web entry site by 07 January 2011.

Photojournalist and Contact Press Images co-founder David Burnett will be chairing this year's jury, which will include, among many others, photographers Abir Abdullah, Vince Aletti, Heinz Kluetmeier, and Getty Image's vice president Aidan Sullivan.

For more details and to enter, visit the World Press Photo website.