From v5.9.0, Images can be dragged into Outline, Map, Chart or Treemap view windows, in order to embed an image in a note. An image cannot be dragged into a note's text window, only into the aforementioned major views. This method is a deliberate workaround for background issues with the v5 text engine (see the last section below) and will be completely revised for v6.
The manual refers to adding to Map view but you can in fact drag a file of any supported bitmap image format - i.e. its file icon in Finder - onto a Map, Outline, Chart or Treemap view.
Be aware that a drag creates a note holding the image, whilst a Cmd+drag (to Map view only) creates a picture adornment.
Image in Note
In v5.9.0+ Dropping a suitable file from Finder into a main view - not into a note window - will result in a new note being created. The title of the note is the dropped file's filename. The content of the note is the image. Bear in mind when doing this that the added file is part of the TBX file and will add to the latter's file size.
Originally, if a note of this type is exported to HTML, the embedded image will be exported as a JPG. The exported image name will include the old extension, e.g. "mypic.png" would be exported as "mypicpng.jpg". This is because Tinderbox is using the note name "mypic.png" stripped of any periods. If the note is renamed after the image is dropped the exported image's name will be the new note's $Name (presumably in 'safe' name format).
A note created from an image drop can still have text added, above or below the image, so this approach can be used to paste an image into a note without having to open the image for editing as would be required for pasting into a text window. The latter method is needed if you want to add more than one image to the note.
Image export is still suspended so images should neither not be placed in notes that will be exported but instead a link to an externally stored image should be used, or a link to such an item be placed alongside the embedded image. Originally, if a note of this type is exported to HTML, the embedded image will be exported as a JPG. The exported image name will include the old extension, e.g. "mypic.png" would be exported as "mypicpng.jpg". This is because Tinderbox is using the note name "mypic.png" stripped of any periods. If the note is renamed after the image is dropped the exported image's name will be the new note's $Name (presumably in 'safe' name format). Image export is still suspended so images should not be placed in notes that will be exported.
Picture Adornment
In v5.9.0+, if you want a picture to show up in a map view as a background picture, then you need to Cmd+drag a suitable image from Finder onto any main view to create a picture adornment. Unless the current view is a Map view the resulting adornment is not seen (i.e. if an image iss Cmd+dropped on an Outline nothing will appear to have happened - switch to Map view to see the image).
Background Issues
The change of text engine in Tinderbox v5.0.0 means it won't accept newly-pasted images. Images in existing documents will, in general, appear normally; some issues might arise. For additional assurance, documents that use images will open as untitled; save them with a new name while preserving a copy of the original. It is intended to re-enable previous functionality when issues with the new text engine are resolved. In the interim, consider using the File button to associate external image files with a note.