Why did YouTube disappear from my Samsung Smart TV?

This happenned on our Samsung Model UN46F7500AF Smart TV purchased in 2013 but the Model began selling in 2012. Speaking to the Samsung support team in USA gives me the feeling that YouTube created a new platform and that the older TV (Prior to 2012) does not support the new YouTube platform.

I will have to pursue this matter with YouTube site for confirmation.

In Summary, the reason YouTube disappeared is not because of Samsung, but because of YouTube's changes.

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