Depends on what app you are using to view the files. Most apps have an option in their "Settings" to show images from "Internal" storage (the phone itself) and/or "External" storage (the SD card). If the app you are using doesn't have this option, then you would need one that does.
Also, it may well depend on the files themselves. Were they photos taken with the phone or files placed on the card from elsewhere? If the former, the phones gallery should recognize them. If they were moved to the SD card from downloads or a computer, etc., then you would need to be sure they are actually files that are viewable on that device.