Backup image smaller than source it's normal ?

hi i recently install the backup&recovery free 17 utility and i made a first backup of a HDD to another External USB Drive.

Source drive holds 750Gb of files but the ackup image only has 625Gb it's that ok ?

I can check some folders but how can i be sure that all files are save ?

thanks for your advice

does not sound like a problem, paragon does compression during the backup, so the destination is smaller than the source, for image or file backups.
when it explodes it back on a restore, it goes to original size.