Sorry, I'm making this a bit confusing.
There are two separate ways that you can set sleep/shutdown images using just your finger.
They start from the Onyx main screen.
This is the screen that has Library/Store/Storage/Apps/Settings as tabs at the bottom.
Method #1 (can only set single sleep images):
Onyx main page > Storage > top big right arrow
Select file with long press, Set as screensaver, [Set as screensaver/ Set as shutdown image]
Method #2 (can also set a group of images as sleep images to rotate):
Onyx main page > Apps > Screensaver
Yes, you can load the images onto your Poke using MTP.
Me, I use ADB for everything. It is more powerful.
You need to enable it.
Onyx main page > Applications > USB Debugging Mode
You will also have to load ADB onto your Mac.
There are probably a zillion links on how to do that.
If you no longer have access to the Onyx main page (because you installed your own launcher) you can still access whatever Onyx had to offer using ADB commands.
For Method #1 (using "Storage"):
Code:
adb shell am start -n com.onyx/.common.storage.ui.StorageActivity
For Method #2 (using "Screensaver"):
Code:
adb shell am start -n com.onyx/.common.setting.ui.SettingContainerActivity -a onyx.settings.action.DREAM_STYLE_SETTING
By "Launcher" I mean the main page when your device starts up.
Here is the one I knocked out quickly when I was sick of the Onyx one.