You, as the client, may dictate poster dimension restrictions'. In X-CD there are no specific poster size format restrictions for the poster dimensions. other than you should maintain a 2:1 ratio between width to height of the poster size.
Posters can contain any form of images or text, but an image file can be stretched or enlarged depends upon its dpi value which stands for dots per inch. A file with low dpi value will get blurred and faded when increased in dimensions beyond a limit.
All ePosters need to be uploaded in a .pdf format into the X-CD system.