The paper cryptanalyses the symmetric key image encryption scheme proposed by Mrinal et al. [1]. The encryption scheme proposed by Mrinal et al. uses Rossler chaotic system for generating three chaotic sequences which are used for creating the cipher image. A secret key of 128 bits is used to generate the initial conditions for the Rossler chaotic system. The equations used for generating the initial conditions in Mrinal et al. encryption scheme have got a loophole. The loophole is utilized to carry out the cryptanalysis on the cipher image generated using Mrinal et al. encryption scheme. Simulation results show that the encryption scheme can be easily cryptanalysed to revealed the exact plain image. An improved version is proposed with statistical and security analyses to ascertain the practicability of the encryption scheme. (C) 2017 Elsevier GmbH. All rights reserved.