We are pleased to welcome you to the 7th ACM Workshop on Information Hiding and Multimedia Security in Paris from July 3rd to July 5th 2019. Over more than 20 years, this workshop (and its predecessors) has been among the main venues where novel and outstanding works are presented and this is the reason why this small workshop is now well recognized in the community. We believe this year is not an exception, with remarkable papers in areas ranging from steganography and steganalysis to forensics and anti-forensics, watermarking and applied cryptography. It should also be noted that the 2019 edition of IH&MMSec will, for the first time in its history, feature two special sessions, one devoted to media forensics and one focusing on the ALASKA steganalysis challenge. This year, the workshop has received a significantly increased number of submissions, to reach a total of 73, among which 10 targeted the special sessions and 63 aimed at the regular track. Their authorship is geographically distributed across Europe, USA and China. Each paper has received at least three independent and double-blind reviews from members of the Technical Program Committee. On this basis, and incorporating the outcome of a paper discussion phase, the Program Chairs have selected the 23 most novel and high quality submissions for presentation and publication. Out of 63 papers submitted to the regular track, the acceptance rate has been kept to 36.5%, in line with previous editions.