Essential secret image sharing scheme with different importance of shadows

•Essential secret image sharing scheme is first formally described.•We give a general construction of essential secret image sharing scheme.•A modified scheme is introduced to achieve smaller size of non-essential shadows.•The essential shadows are more important than non-essential shadows.

In (k, n) secret image sharing (SIS), a scheme encrypts a secret image into n shadow images. Any k or more shadow images can be collaborated together to reveal the secret image. Most of the previous SIS schemes don’t distinguish the importance of shadows. However, in some application environments, some participants are accorded special privileges due to their status or importance. Thus, some shadows may be more important than others. In this paper, we consider the (t, s, k, n) essential SIS (ESIS) scheme. All n shadows are classified into s essential shadows and (n–s) non-essential shadows. When reconstructing the secret image, the (t, s, k, n)-ESIS scheme needs k shadows, which should include at least t essential shadows.