The K25 suffix indicates raw image data generated by the digital Kodak DC25 camera.
The K25 files contain the unprocessed or minimally edited raw data of the image sensor. Although these RAW (raw) data are larger than the JPEG files stored by the device, they are more versatile.
These sometimes called "digital negative" raw data are excellent for post-processing such as the adjustment of the colors, correction of the exposure, suitable for sharpening or noise filter. They are indispensable for professional work or things like astrophotography.
In order to convert them into an RGB image format that can be commonly used, the data must be "developed". This means that processing steps such as interpolation and exposure as well as converting to a format such as PNG, PSD, TIFF or JPEG must be performed.
Most RAW files also contain metadata with information about the image and the recording conditions, in part also in the EXIF or IPTC standard.