I believe if you want to use the Bullets & Numbering to create your bullets automatically you'll need to have the green leaf image in the form of a font. There are some freeware software programs out there (Google to find one that will work with your operating system) that can help you transform an image to a font. Then you can add the font to your system and put the "bullet" into use through the Bullet & Numbering options (found under the menu on the Paragraph panel).
Another option that may be less complicated in the short term if you don't have to use the green leaf too often is to insert the image as an anchored object. Then each instance will move with the text as you make edits.
Hope that helps a bit!
I would go with the anchored object option but even easier is to use the graphic as an inline object (a form of anchoring). Size the graphic to the right size, copy and paste it into the text. You can use the up/down arrows to center the graphic on the line. Use tabs to set the space between the graphic and the item it's the bullet for.
Our own Jongware has written the VERY nifty script to turn any black and white vector art (you can trace the leaf in Illustrator, and change the color to black there, if you need to convert it) into a custom Open Type font WITHIN Indesign. He posted a demo version that does a single glyph at http://forums.adobe.com/message/4518080
I've used it for custom bullets for a couple of clients, and it's fantastic.
I should have known. Great script!