Generally, Tinderbox expects bitmapped images of the JPG (JPEG), GIF, or PNG format. Tinderbox will likely accept other older formats such as BMP, PICT but these are best avoided if possible.
Formats used as wrappers for bitmap content, are not supported directly, but can be used indirectly as discussed below. For instance, more complex bitmap formats such as TIF/ (TIFF) which can support a wide of complex internal formats (hidden from the ordinary user) may work depending on the internal structure of the file.
In general, if you can open an image with Preview (or some image editor such as Graphic Converter, Lightroom, Aperture or Photoshop), you can select a portion of that image, copy it to the Mac clipboard, and paste it into Tinderbox as an image adornment (though not as an image note). The latter applies to PDF and TIFF files, among others.
Apple Preview and image editors can also convert TIFF files to JPG or other simple bitmap formats files that can be dragged into Tinderbox as image notes.