Exactly half of the witnesses to the Hillsborough disaster sought by Operation Resolve have come forward.
Since the latest appeal was launched last month, 21 people out of 42 have been successfully identified from the gallery of images.
The pictures released by Operation Resolve are of people who assisted some of those who tragically lost their lives on April 15, 1989.
Although the images are 26 years old, it is hoped that the public will recognise these people and will contact investigators to identify them.
The public are asked to visit www.operationresolve.co.uk to view the gallery of pictures and they can also call Operation Resolve on 08000 283 284, if they can identify an image.