I use dd for a similar job.
But in my case it was an bootable windows 7 sdhc card.
Code:
root@kali:~#dd if=/dev/sdb1 of=/root/Desktop/win_install_sdcard
Try
Code:
root@kali: file card.img
If i do this with my win_install_sdcard
It says:
Code:
root@kali:~# file win_install_sdcard 
win_install_sdcard: x86 boot sector, Microsoft Windows XP Bootloader (4.german), code offset 0x58, OEM-ID "MSDOS5.0", sectors/cluster 16, reserved sectors 2242, Media descriptor 0xf8, heads 255, hidden sectors 2048, sectors 31289344 (volumes > 32 MB) , FAT (32 bit), sectors/FAT 15263, reserved3 0x800000, serial number 0xe611f86d, unlabeled
and I mount it with:
Code:
root@kali:~# mkdir /mnt/tmp
root@kali:~# mount win_install_sdcard /mnt/tmp -o loop
Now if you want to find jpeg (or other) files in it, try:
Code:
root@kali:~# find /mnt/tmp -name "*.jpg" -print
And just change "*.jpg" to the filetype you want to find.

Or you change into /mnt/tmp and search on your own.

Greetings

Chaos