OJS 3.1.2 includes support for iThenticate plagiarism check the Crossref Similarity Check service.
https://github.com/asmecher/plagiarism
For this plugin to work, the following must be added to your config.inc.php file:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; iThenticate Plugin Settings ;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
[ithenticate]
; Enable iThenticate to submit manuscripts after submit step 4
ithenticate = On
; The username to access the API (usually an email address)
username = "user@email.com"
; The password to access the API
password = "password"
Additionally, SimCheck full-text urls will be provided to Crossref as part of the DOI submission process automatically.