Question: We're currently trying to optimize our site so the end users get fast response times. One of the areas we are looking at moment is the media served from the Sitecore Media Library.

What settings are available and what techniques can be used to ensure that the media items are both optimized in terms of size?

For example, it's not uncommon for users to upload large high quality 1MB+ images, but the image may only used as a small thumbnail on a related content widget or even when used as a main image on a page, the uploaded image is much larger than the conataining HTML element.

Are there any settings available to "down size" the image for each use or should be instead ensure that the editors upload the correct size image to begin with?

Answer: 
You could also use this...

<https://github.com/kamsar/Dianoga>

An automatic image optimizer for the Sitecore media library.
If your question re DAM selection is still open then I would recommend to consider building your external asset management based on [Amazon Web Services](https://docs.aws.amazon.com/general/latest/gr/Welcome.html) and then plugging it into Sitecore.

I have recently released an open source module called "External Asset Management in Sitecore" what does all the integration routine, it is available on GitHub [here](https://github.com/kate-orlova/external-asset-management-in-sitecore) and I hope that you will find it helpful.