To copy them, possibly, but you want the data that the app is keeping, not the app itself, and you can't access that from the PC. You might be able to access it using VNC, but you'd have to install a VNC server on the phone first - for which you'd need access to the screen.
(This is one reason that ALL your data should always be backed up to another device or cloud account.)
I'm assuming you know what the app is called? Look in the Play store or maybe even the app developer's website. See how the hidden files are stored. Some of those apps just move the images to a hidden folder. If that is the case then you can probably find that folder in your phone's file system via your computer.
If the app encrypts the images then maybe you can download the encrypted files to your computer. Then install the app on a new device & transfer the encrypted files over to the new device. Hopefully the app will still be able to read them.
Ultimately, your best bet is probably going to be to contact the app developer & ask them for advise. But, I agree with Rukbat, always, always make sure there is a back up!