Android : How to efficiently manage image resources, both local and networked, in Android?

I am working on an app, which requires-

1. Pull contact details and images from the local contact book.


2. Some interval apart sync this contact data (all of it) to a server.


3. Pull contact data (images as well) from the server whenever needed.

I basically know how to implement them individually. For example, I have already managed to pull local contacts, I am yet to achieve 2 and 3. I have few questions regarding them.

1. Where do I save the images (both local and networked)? Do I need to save them in any particular folder? If yes then what is the recommended way of doing that?


2. I have used volley library in another project, and I am hoping to use it again here. AFAIK, volley caches networked images in the memory. But I believe that in my app, there can be users who will have more than 2000 contact data. My intuition is that not all the images will remain in the cache for ever, so if I want my app to work offline, I will need to images to be stored locally. I am confused about where to store the images and how to achieve that. Point to note, this app will be accessed frequently.


3. What is the recommended way of sending image data over the network to a server.

The questions may seem broad, but I feel that they are tightly coupled, considering a single app. I am expecting expert opinion on the recommended ways of achieving these features.

Thanks!