Generally, such date based notifications are implemented in filemaker with a script set to run when the file is opened. The script would perform a find for all records that are within x-days of expiring. If any such records are found, a message is displayed listing them and warning the user that the images are nearing expiration.
The exact details will depend on the structure of your database table where you store your images (or references to their files).
There are also ways this script can be set to run when a specific account name is used so that other users to whom the warning message does not apply don't see it.
How do you make a script to do this?
In File Options, you can select a scrip that will be performed when the file opens.
Say you want to be alerted of all files who will expire in 5 days or less...
Go To Layout [ImageTable]
Enter Find Mode 
Set Field [ImageTable::ExpirationDate ; ">" & Get ( CurrentDate ) - 5 ]
Set Error capture [on]
If [ Get ( FoundCount ) > 0 /* expiration records were found */]
Sort Records [no dialog ; restore] //specify a sort order that makes sense to you
Show Custom Dialog ["These images will expire sometime in the next 5 days"]
Go TO Layout [//select the layout you expect see if no expiring image records were found]
This is a bare bones script. There are lots of ways to enhance it. In particular, there are ways to tag the records if you don't want to keep seeing them listed after the initial warning message appears.