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You will need to create a folder on your computer's desktop. Put the pictures you wish to hide in the folder on your desktop. This is the first area in your phone's internal memory, and it contains several things, including app data. Open up your start menu and navigate to "This PC." Locate your device, and click on it to open. Drag and drop the folder onto your phone's icon. Once you've transferred the folder, disconnect your phone. Using a file manager app, rename the new folder to something else. Make sure it has a period (e.g., .appicons) in the beginning. This makes the folder visible to you but not to Android. It also makes it look like it's a system folder, so it isn't conspicuous. You might want to name the folder something related to an app rather than pictures. Go to your Gallery app. Scroll down and try to see if the folder appears in the Gallery. It should not be shown in the Gallery if the file-naming was done correctly. To make the folder appear again, head to the file manager app and go to "Settings." Tap on "Show Hidden Folders" to reveal those hidden, then simply remove the period preceding the folder name to reveal it to the system.
Create a folder. Organize your images. Place the folder in your internal memory's root directory. Rename the folder on your phone. Check your pictures. Unhide the folder.