The easiest way to make an image editable in Taxi is to wrap the <editable> tag around the image tag.
<editable name="" label=""><img src="http://placehold.it/640x300" height="300" width="640" border="0" alt="alt text"></editable>
However sometimes you may need to break this tag apart, whilst maintaining content that has already been added in Taxi using the Design System. You can do this by adding fields for image source, width, height, alt text and anything else you may wish to add.
<editable name="" label="">
<field type="src" name="src" label="Image Source"></field>
<field type="number" name="width" label="Width"></field>
<field type="number" name="height" label="Height"></field>
<field type="text" name="alt" label="Alt text"></field>
<img replace-src="{{src}}" replace-width="{{width}}" replace-height="{{height}}" replace-alt="{{alt}}">
</editable>