How to query email and images from feedItems in case object?

Query like:

select Id, Body, isRichText, Title, Type from CaseFeed where ParentId = '50090000008cXoS'

where

If Type = ContentPost, then it is an attachment. Then check for ContentType of the file

if(contenttype =='image/jpeg' || contenttype=='image/png' || contenttype=='image/gif' || contenttype=='image/jpg' ){ ... }

If isRichText = True, parse the body to check for email ids.

Hi

I am not able to do this can you explain me how to get parentId.

Thanks