Just to add, that DCIM folder is what you should keep in mind for everything photo-related. The DCIM folder, or Digital Camera IMages, is the default storage folder for photos. We (as in we, the consumer) are really, really lucky that DCIM is pretty much the default place for not just different apps but different platforms. Even Apple, notorious for not following standards and norms, has opted to stick with DCIM folders as its default photo library folder. So do point your phone's camera to automatically store your photos into that DCIM folder on your microSD card, and use that same folder to save photos that get downloaded from apps like your browser, texting, Twitter, Facebook, etc. Having a central place for all your photos make it easier for you to manage your photo library.
Something you should seriously consider is to install an app like Google Photos:
https://play.google.com/store/apps/details?id=com.google.android.apps.photos&hl=en
You can use it as a substitute for the Gallery app, the Android default photo manager, but what's much more important is the Google Photos app includes an automatic backup and sync function. Never rely on your smartphone as the sole location for your photo library, besides the fact it can get lost or stolen, no smartphone is 100% reliable or even close to that. The operating system can become messed up or the phone could get damaged by an accident, and to top it off, the file system that microSD cards use is proprietary, outdated, and only marginally stable (It's a variant of Microsoft's no longer supported FAT file system). So microSD cards themselves are physically stable but the file system that they use is easily corrupted and not very robust.
Anyway, all this boils down to is that back ups are really important. Google Photos will back up your entire photo library into your online Google account. With your photo library backed up online, whenever necessary you can access anything in your photo library either on your phone or remotely by logging into your Google account on a computer browser:
https://photos.google.com