Many Swf Packager tools (KuneriLite, SWF2Go, Janus) use SVG-t as their primary icon format.

With these instructions you can use also PNG file easily:

1. Convert the PNG image to base64 format from here.

(Press “Browse” to select the file and then “Convert”)

2. You’ll see “Base64 representation of the source data”
Copy and paste the entire textfield into some text-editor.

3. As SVG is basically text file, we can directly use the Base64 formatted text.
Use the template text below to create your SVG (replace the text
THE BASE64 ENCODED BITMAP GOES HERE with your copy pasted text) :

<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="http://www.w3.org/2000/svg"
xmlns:xlink="http://www.w3.org/1999/xlink"
contentScriptType="text/ecmascript" zoomAndPan="magnify"
baseProfile="tiny" contentStyleType="text/css" version="1.0"
width="6.77196" preserveAspectRatio="xMidYMid meet" viewBox="0 0 6.77196
6.85856" height="6.85856" fill-rule="evenodd">
<g>
<metadata/>
<g>
<image x="-2.847" y="-3.71656" transform="matrix(1 0 0 1
2.847 3.71656)" width="6.77196" xlink:href="data:image/png;base64,THE
base64 ENCODED BITMAP GOES HERE" xlink:type="simple"
xlink:actuate="onLoad" height="6.85856" preserveAspectRatio="xMidYMid
meet" xlink:show="embed"/>
</g>
</g>
</svg>

Now save the text file and convert the SIS.
No more hassle with Illustrator, Inkscape and SVG2SVGT Converter !
However, your bitmap icon will not be scalable, so stick to SVG if you are targeting more than one device model.

Kudos to Riku Salminen/FN for the hint!