Movie poster have been used since the earliest public exhibitions of film, at the end of the 19th century. It was then the main promotional tool for a movie, in which studios invested large amounts of money, using best artists to distinguish their movie from competitors.
Illustration instead of photos was far more common, prior to the 1990s. Photos were introduced in movie posters from late 1950s, because they were cheaper ; but they also allow less artistic originality (even if some photomontages are really beautiful).
Trailers, radio, TV and internet has also widely contributed to movie posters depreciation as a promotional tool. Indeed, why investing in a beautiful poster when you can be on TV news ?
Moreover, advertisers have more and more put aside artistic consideration, to concentrate on well-known marketing techniques aiming to fill movie theatres, like a close-up of the movie star, with a sharp look and heroic posture, a background color depending on movie genre (white for comedy, black for thriller..), going as far as pretesting the visuals on a representative public sample...
All this explains the general tendency to visual standardization, and the collectors taste for the originality of elder movie posters. It also explains why we mostly propose elder documents in our catalogue, with some exceptions, like these beautiful "advance" english posters of Black Swan (2010) :
However, visual standardization is the major tendancy. And because sometimes a picture is worth a thousand words, here is a great poster setting from the blog of Christophe Courtois :
Apart from the visual standardization, movie documents (including movie posters) are exposed to growing digitalization of promotional tools, of which famous producer George Lucas is a fervent supporter. Indeed, all movies being already digitalized, why won't it be the same for their promotional tools ? Besides, numerous press kits are already sent on digital medium. And it is foreseen that in a near future, movie posters will not be displayed in movie theatres, but screen shown.
To conclude, it seems that we are witnessing the slow extinction of "paper" movie posters, and of paper documents in general. Fortunately, the movie poster market is still in great shape, thanks to collectors more numerous and willing to preserve this unique historical heritage.