This study presents an expandable essential secret image sharing structure
showing that some important shared images, named essential ones, are necessary when re-
covering the secret image and the proposed structure must incorporate other secret image
sharing scheme to expand to a new secret image sharing scheme with multiple functions.
An (s, t, n) essential secret image sharing structure shares a secret image with two kinds
of shared images, essential and non-essential ones, and the total number of shared im-
ages is n. Two criteria must be met to recover the secret image. Firstly, the number
of essential images must be at least s. Secondly, the number of collected shared images,
including essential and non-essential ones, must be at least t. An essential participant
holds his secret key as a conventional secret key concatenated by a shared essential key.
The shared image for a non-essential participant is the XOR result of a correct shared
image and a disturbed image generated from the essential key. Experimental results re-
veal that the proposed method distinguishes essential and non-essential shared images,
and keeps the threshold on essential shared images in recovering the secret image.
Journal of Information Hiding and Multimedia Signal Processing 7(1), pp.135-144