Hi,
If you have many images and / or they are big 100kByte+ you should keep them in a subdirectory and ship the wiki with the directory. TW allows relative links, which also work well from a "file" TW. A "file" TW is a wiki that is on your local drive and you start if from there.
If you use the _canonical_uri field, the tiddler contains meta data only, but if you transclude it, or use it with an [img[link]] the system will treat it, as if it is an image.
eg: You can have a note-1.png in a directory eg: images
your Tiddler would look like this
title: note-1.png
_canonical_uri: ./images/notes-1.png
type: image/png
If it is a jpg it would be
title: note-1.jpg
_canonical_uri: ./images/notes-1.jpg
type: image/jpg
Image types that are part of TW are: jpg, gif, png, ico and svg. SVG is a vector graphic format and the others pixel graphics.
So the tiddler note-1.png only needs some bytes in the wiki. If it is shown, TW dynamically loads the content form the harddis.
have fun!
mario