CMYK and RGB are two different color models for different on displaying and output platforms: The four-colour model CMYK (Cyan, Magenta, Yellow, Black) is used for the definition of unique hues in the DTP and printing sector, whereas screen colours are mixed with red, green and blue (RGB).
(For Black there is on RGB no or a ’zero’ value; on this part of the screen the monitor tube beams no light (=zero), activates no chromatic spectrum and stays black. In contrast to it however no colour in printing office means - on white paper - especially white.)
The resolution of both media are likewise different: a computer screen shows images with 72 dpi (dots per inch), in offset printing pictures are brought on the paper with high-resolutions (350 dpi or more e.g. in the art print).
Press service: The photos offered here for download are primarily as service for the press. So clear target medium is first of all the DTP / prepress sector.
The high-res photos for downloading (mostly with "...cmyk300.jpg" at the file end) are generated with high end scanners, edited an used for printing CD covers or posters mostly in CMYK. (Some are in RGB; please convert them to CMYK)
As file format we have chosen JPG (without additional compression) instead of Tiff or BMP (Bitmap): the file sizes are no so large for downloading them via internet. For a prepress production process you better save them as Tiff.
Displaying errors: JPG is coincidentally also a format for pictures on web pages. During the installation internet browsers often are unfortunately registered in the OS as the default program to handle files with the ending *.jpg instead of leaving them to a DTP or picture editing program like Photoshop or Gimp.
With a doubleclick on a file downloaded here e.g. the Internet Explorer starts and shows the picture only rushed or with vertical stripes, since originally the browser is capable only of displaying RGB pictures with 72 dpi.
This is however no error in the file but mandatory - due to the target medium print / press described above. For displaying the pictures on computer screens they can be converted problem-free into RGB and 72 dpi with every usual picture editing program into RGB with 72 dpi.