This method links stream object to an existing file:

Method imagefile()
{
  set obj = ##class(Sam.binary).%New()
  read "enter path to image: ",img
  set st = obj.Image.LinkToFile(img)
  write $System.Status.GetErrorText(st)
  set st = obj.%Save()
}

Please post your class definition here.

Yes.

Should the user enter the path to the existing image?

Looks good.

1. Define your collection property like this:

Class collect.arraylist Extends %Persistent
{
Property DOB As Array of %Date;
}

Instead of "Array" you can also use "List". Documentation.

Great article, however, I strongly disagree on the testing tools choice. Curl is not really the option, as CLI tools are really not the best for json editing. Upon the rest of your testing suggestions, I think there are better alternatives, such as:

• REST clients: “Advanced REST Client” for Chrome and “REST Client” for Firefox, some are also available as a standalone applications
• Debugging web proxies: Charles, Filddler etc. for the rare cases where REST clients do not offer enough information

For each can be implemented via macros:

#define ForEach(%in,%gn) s gn%in=$na(%gn) s %in="" f { s %in=$o(@gn%in@(%in)) q:%in=""
#define EndFor  }

$$$ForEach(key, "^global")
    Write key,!
$$$EndFor

What do you want to do with it?

Ensemble settings can be specified for a namespace. So you specify common setting values (or defaults) in production class, and in a SMP you define the instance-specific settings.

The problem I see here is, if only one of the data object's properties has changed, how do we know which? Or do we simply overwrite all properties? 

If you use old json classes, you can send only changed properties, for example this json payload would be converted into  Sample.Person object with id=1 and all properties taken from disk except for Name property, which would be set to Bob:

{ _class: "Sample.Person", _id: 1, Name: "Bob" }

With new json you can get dynamic object from json with only modified properties and change persistent object by iterating over defined properties of a modified object.

I usually write Abstract REST class for handling all REST technical checks and conversions, and inherit all the other REST brokers from it, so they only contain logic related to calling business logic and outputting the results.

Request -> Abstract REST -> REST -> Business Logic -> Data

For example check this abstract broker for json->obj conversion example.

Here are some articles on community about that:

• Free Text Search by Kyle Baxter
• iKnow demo apps (1, 2, 3, 4) by Benjamin DeBoe 

• Session Cookie Path - Scope of the session cookie. This determines which URLs the browser uses to send the session cookie back to Caché. If your application name is myapp, it defaults to /myapp/ meaning it only sends the cookie for pages under /myapp/. If you restrict this to only what is required by your application, it prevents this session cookie being used by other CSP applications on this machine, or from being seen by any other application on this web server. On the other hand, browsers and cookies are case sensitive. Setting the session cookie to '/' can prevent license or session problems if, for example, an application name changes from capital to lowercase letters.
• Login Cookies hold information about the most recently logged-in user. If you want to keep your users from having to log in too often, but you want your applications to remain distinct and unconnected, use Login Cookies.

As every BP is also a SQL table, you can select active processes which are older than 1 day  with this query:

SELECT ID, %SessionId, %SuperSession, %TimeCreated, DATEDIFF('day',%TimeCreated, CURRENT_TIMESTAMP) AS DaysOld
FROM <business_process_table>
WHERE DATEDIFF('day', %TimeCreated, CURRENT_TIMESTAMP) > 1
      AND %TimeCompleted IS NULL

As BO messages also get logged, you can check Ens.MessageHeader table for message processing time.