[rkomar]

The /dev/loop5p* devices listed by fdisk don't actually exist on your system (i.e. the linux kernel doesn't know about the partitions in the image file). You need to tell mount where the partition is within the image file by providing a byte offset to it. From the fdisk listing, the first partition starts at sector 6819584 with 512 byte sectors, so its byte offset is 6819584*512 = 3491627008. You should be able to mount the partition with:

mount -o loop,offset=3491627008 /dev/loop5 /mnt/sdx1

However, I can see that fdisk reports that flash.img is 541 MB in size, which is too small for what the partition table inside it reports (it looks like it should be 4 GB in size). If the flash.img file really is only 541 MB in size, then the mount command I gave above will fail because the byte offset points past the end of the image file. The start position of the first partition also appears to be wrong. It should be one sector after the end of the last linux partition, i.e. 1009664 (not 6819584). I think you may need to re-read flash.img from the ereader's SD card to start again from correct values.