You can try associate the file type in question (JPG?) with the application that you edit them with and then open them through a network capable file manager such as ES Explorer and hope that the application likes that. There is a high chance however that it does not.

If not, you need to mount the network folder as a normal folder on your device. Then your app will think it's a local file and will do it. Keep in mind that this might be significantly slower than having the file locally on your device.

Since this is not as easy to do as in Windows where the mounting of network shares in built-in, you have to hack your way a bit towards it. The first thing what you need is Root access to your device. Then you need a tool to mount like the mount manager. and the there described sub-modules.

Keep in mind that the mount manager requires specific kernels to work. In the end it is a question which android hardware and kernel you have. You can search on the app market for "mount" and see if other tools come up that you can use in case mount manager does not work for you(r device).

I would highly recommend you to move over to either android.stackexchange.com or xda-developers.com to get help there specific to your device and its currently installed operating system, asking a question such as "How can I mount network shares as local folders on my [phone model] running [OS version].

While this is not a complete answer, I hope, given the fact that I do not know your phone or operating system, you get the right direction to do that.

As an easier workaround you can still use a service like a file sync tool and sync only the files that you are working on right now, assuming that you do not need to work on ALL your photos 100% of the time.