From TRC Data Recovery:
Chk-Back data recovery software can help restore data corrupted by the Windows CHKDSK process. If data is lost during CHKDSK (check disk), this utility can scan these individual files to determine if the files are useable, if the software is able to recognise files it will then create a copy of each file within a directory where the original CHK files are stored. Most common file types are supported: jpg, bmp, jpg, exe, png, dwg, qbb, mp3, rar, mp4, wma, mpg, pdf, gif, mid, xml, tif, mso, avi, wav.
This application allows users to select a specific directory containing CHK files using a user friendly interface, a few clicks later the application will interogate each file and determine if this file contains useable data, if the file type is recognised then a copy of this file is created within a new directory within the original, this application DOES NOT change the original files in any way, the files are tested then a copy is made if the file type is recognised. In some instances the file type can be recognised but corruption can cause the file to be unuseable. It is not recomended that Chk-Back is stopped mid way through a scan.