Cyanotype is not a word many may be familiar with, though the defining blue-hued photographs that the printing process creates is easily recognizable and distinct. The prints themselves, with their cyan tone (hence the name) can be picked out of a crowd easily and are beloved by many, yet, until now, no major United States exhibition had ever given them their proper glory. That all changes with the Worcester Art Museum’s “Cyanotype: Photography’s Blue Period,”exhibition. This is the first fully realized exhibition in the country, ever, with a formal opening event on Feb. 18.