Semiotics

There are several features and connotations used in this image to allow the audience to have a clear understanding of the themes, genre etc. without them necessarily noticing.
Firstly, the characters appear in an order, with the main character in the center of the page who is also the largest person there. This is also seen by the order of actors listed at the top of the page and these are listed in order of importance. This already indicates to the audience who the main characters are before even seeing the film. You can also see who the main character is as swords are acing like a frame to his face, making him stand out more than the rest.
This could help them to also know the genre because an actor/actress who is appearing in the film may be known to star in certain genres. However with this image, that isn't the case. In this instance the genre can be seen by the mise-en-scene. For example, the bandanna on Johnny Depp's head, the two swords he's holding and the pirate ships all indicate the swashbuckler genre to the audience. Even as little as the facial hair and jewelry can be used to identify the genre as we expect to see pirates wearing large rings, hats and have facial hair which is primarily a mustache.
There are mainly dark colours used which is associated with mystery which is a common convention among the swashbuckler genre. The use of the colour red can also indicate to the audience the danger which will occur. This suggests that there is a lot of violence within the film.
Although the conventions suggest that this is a dark, violent film, the fact that we see the 'Disney' logo at the top of the poster, this allows the audience to see that the film is actually family friendly and suitable for the majority of people.