With the latest firmware release for the Slingbox 500, the "SlingProjector" feature within My Media can now project both still pictures AND videos from your iPhone, iPod touch, or Android phone.
Be sure you have the latest version of SlingPlayer for your iPhone, iPod touch, or Android smartphone. Then, when you're in the same wireless network as your Slingbox 500, tap My Media from the SlingPlayer main screen. Tap a photo album ... and enjoy viewing your pictures and videos on the TV that your Slingbox 500 is connected to!
Note that the SlingProjector features (photo & video) work ONLY IF BOTH SlingPlayer on your phone AND the firmware on your Slingbox 500 are fully up-to-date.
If that's not the case, then you'll see an error message either on your phone, or on your TV interface (depending on which needs updating).
Here's an FAQ that you can look at for more information: