What is Amazon Web Services Greengrass?

It is a software solution to run local compute, messaging, data caching, syncing, and have Machine Learning inference capabilities.
Using AWS Greengrass connected devices (as in IOT for example) can run AWS Lamda functions, keep device data in sync and communicate with other devices securely in the Internet's unconnected scenario. This way using local compute you can interact with local resources, intermittent connections and updates with air updates.

AWS Greengrass involves both local resources as well as AWS. The development uses the same programming languages.

AWS Greengrass can:

• filter data so that only necessary data is transacted to the cloud
• Authenticates and encrypts device data at all points of connection(using AWS IoT Core)

Here is a  video how AWS Greengrass works.
Source:https://aws.amazon.com/greengrass/ 


Benefits:

• Respond to Local events in Near Real-time
• Operate off line
• Reduce the Cost of running I0T Applications
• Simplified Device Programming with AWS Lamda

Nokia's Multi-access Edge Computing (MEC) together with AWS Greengrass addresses the Enterprise use-case such as off shore Oil Exploration

https://networks.nokia.com/solutions/multi-access-edge-computing

What is a good size for an image to display on a Smart Phone?

This is a very broad question. Of course, 'Smart Phone' narrows it down somewhat. However there is still a large range of phone sizes. The following are my observations and should be tested in each case.

I had a need to place couple of dozens of images in an app (generic). I was developing the app with IntelXDK using just with HTML5, actually a web app. I wanted to make sure that I could fit in the images in my app. But what size? what file size? 

I experimented with the images you can take with a smart phone (1028x768) and resized images 75%, 50% and 25%. On an emulator they look the same. I had to set the size on the IntelXDK designer so that I can see the images properly on some of smart phones.

The details are here:
This next part (Part 6) is all about placing images and text formatting:
http://hodentekmobile.blogspot.com/2016/02/develop-side-menu-app-using-intel-xdk.html
Apple iPhone 6

 Apple iPhone 5

 Motorola Razor

 Nokia Lumia 920

 Samsung Galaxy S