If you have a few .img files coming as disk images from devices like floppies, CDs, DVDs, SD cards, etc, you will realize that you cannot mount the in Linux, because they contain a file system that has to be mounted.

In linux you would need to use the mount command as for any physical device, however you need to know the correct syntax that is based on understanding the information related to the partition(s) available in the image.

First step is to read the partition Start point using fdisk:

Pull up a bash prompt and execute:

sudo fdisk -l imgfile.img

You will see something like this:

Disk imgfile.img: 28.99 GiB, 31104958464 bytes, 60751872 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x6c586e13

Device                   Boot  Start      End  Sectors  Size Id Type
dan-octopi-20210407.img1        8192   532479   524288  256M  c W95 FAT32 (LBA)
dan-octopi-20210407.img2      532480 60751871 60219392 28.7G 83 Linux

As you can see there are two partitions, one that is FAT32 and the other one that it’s ExtFS. This means that to mount the first partition we have to tell Linux that we need to start at the sector 63. Note the sector size is 512 bytes, so to read/modify the data in the first partion:

sudo mkdir /mnt/disk1
sudo mount -t vfat -o loop,offset=$((8192 * 512 ))  imgfile.img /mnt/disk1

where:
8192 is the start of the first parition
512 is the sector size

H/T: https://stefanoprenna.com/blog/2014/09/22/tutorial-how-to-mount-raw-images-img-images-on-linux/