Custom images must be in PNG format. Transparency is recommended for best appearance. Images will automatically be reduced in size to fit whatever button or location is used.
Your custom images can now simply be added to your photo library and you will see them as options when choosing images. Once you have imported an image using the photo library, it is part of your configuration and you may delete it from your photo library without impact. Images that are part of your configuration can be deleted from the configuration by using a long-press or right-click (depending on your platform) on the image in the custom image selection panel.
Images will be re-colored to match the location they are used. In general, using one solid color is the best way to construct images you wish to use for Activities.