2.2.14 [HTML5] Section 4.7.1 The img element

C0019: Images are obtained immediately

The specification states:

 ... The img element
     ...
     In a browsing context where scripting is disabled, user agents may obtain images 
     immediately or on demand. ...

All document modes (All versions)

Images are obtained immediately.

C0020: An unavailable image indicator is shown to the user when no image is available

The specification states:

 4.7.1 The img element
     ...
     What an img element represents depends on the src attribute and the alt attribute.
  
         If the src attribute is set and the alt attribute is set to the empty string
             ...
             ... User agents may provide the user with a notification that an image is 
             present but has been omitted from the rendering.

IE10 Mode, IE9 Mode, IE8 Mode, IE7 Mode, and IE5 (Quirks) Mode (All versions)

An unavailable image indicator is shown to the user when no image is available.

C0021: No image indicator is shown when the image is unavailable

The specification states:

 ... The img element
     ...
     What an img element represents depends on the src attribute and the alt attribute.
  
         If the src attribute is set and the alt attribute is set to the empty string
             ...
             ... User agents may provide the user with a notification that an image is 
             present but has been omitted from the rendering.

IE11 Mode and EdgeHTML Mode (All versions)

No image indicator is shown when the image is unavailable. If alt text is available that text will be shown.

Show: