Facebook share button with custom parameters will help you to post custom image, title , descriptions, url , caption etc.The First option is sharer.php that have all this facility and its works fine up to last week , but unfortunately its override with basic like function ie, when you pass custom param to the sharer.php it reads the custom url you provide and took information such as image,title meta details from that page.
While playing with facebook old share.php I noticed few things, it will not work properly with canonical urls(Duplicate content avoiding option). When we try to pass url to the sharer.php it reads the meta content and look for the canonical url then parsing correct url as canonical url. So sharing image and description are different than you saw on the share dialog box.
I search on Google for this issue and finally found Facebook shows some wrong image and details in the dialog box but sharing time it parses the actual url. This means the sharer.php is not works like what we expected.Then I found an alternative way for share button with custom param.
Create an APP and use the feed dialog method of Facebook. First you have to sign in and move to Developer portal. Choose create an app and set proper details do not forget to set siteurl.
after you create FB app you will get an APP ID keep that and follow the scripts. Add the following codes in your page header section.
Then just use the FBShareOp() for triggering the share button, you have done with Facebook share button with custom parameters, make sure you added APP ID in your program. Also you can debug your url using Facebook Debug Tool.Note :
Keep in mind Facebook or any social media’s are not stable they updated their coding strategies any time so keep an eye open on your social media scripts otherwise it will break your application.