Transposition based symmetric encryption and decryption technique for secured image transmission through internet The role of internet became a non replaceable one in our day to day life. Internet users also face various security threats such as eavesdropping and unauthorized access through intrusion. Internet users need to be protected and provided privacy. Network security and image encryption has become important and high profile issues. Various cryptographic techniques are already available in literature for secured data transmission. Image encryption is still a major area of research with extensive effort being spent in determining a standardized image encryption technique that is difficult for hackers to crack the image. Hence the proposed work aims at developing an effective and standardized image encryption technique. At the transmission side it involves the following steps: subdividing an image in to n number of sub images of p × q, finding a suitable permutation/combination to interchange the pixels, merging the sub images in to a single image and transmitting it. At the receiver side the received encrypted image is subdivided in to n number of sub images of size p × q, the original pixel positions are obtained and the original image is formed. The effectiveness of the technique is measured in terms of correlation index and entropy for different rules of permutation. Finally the most effective permutation is identified which results in lesser correlation index and stronger entropy. The computational complexity of the algorithm is also analyzed.