Yes the .img files should be restorable with dd but you can also do it from the disks tool itself if you are less confident with the command line.
To restore using the disk tool , select the partition you want to restore to , click the cog and select 'restore partition image'
If you are unsure about the type of a file you can check it using the 'file' command, this knows how to recognise pretty much any file format.
heres the output from an image i took of a windows restore thumbdrive using gnome disks. We can see that its a whole disk image because
amias@rome:~$ file windows-restore-thumbdrive.img
windows-restore-thumbdrive.img: DOS/MBR boot sector, code offset 0x58+2, OEM-ID "MSDOS5.0", sectors/cluster 8, reserved sectors 2306, Media descriptor 0xf8, sectors/track 63, heads 255, hidden sectors 2048, sectors 15628288 (volumes > 32 MB) , FAT (32 bit), sectors/FAT 15231, reserved 0x1, serial number 0x1e112916, unlabeled
To restore using dd to the fifth partition of the second disk (/dev/sdb5):
dd if=yourimage.img of=/dev/sdb5
You can only create images of a partition using the disk tool and not an entire disk.
Don't forget to update your boot loader after changing your disks if you want to boot from them. For the vast majority of cases this is done by running :