difference between image (database) field and image (filename) field

somone can tell me what is thedifference between image (database) field and image (filename) field in SC?

If you set the field to database then you need to map a database (blob) field to store the image. Otherwize the image will be uploaded to the configurated directory.

Thank you very mach for your answer,
i have used the image(file name) field.
is there any limitation for the number of image (files)? or the image size?
because i have to upload dicom images to a patient, and each image is about 527 KB, i have 138 images for each patient. When i run the multiupload (CTRL+A in the source directory: 138 files) and drag in the upload zone; some of images are not uploaded ie i have only 35 file uploaded (in destination directory).

Do you have any recommandation about which way to use ? Is that better to use BLOB ? Ex. To store the picture of each team members.
Thru Scriptcase, is that possible to compress the upoaded image before instert in the database ?