When you submit a lot, pictures are optional. Before you skip them, though, take a look at these graphs.
These charts are based on 374 lots sold in three different TFCB auctions. First, here's how having a picture (or not) changes the sale price:
Interestingly, not having a picture doesn't make much difference in determining how much your lot will sell for (look at the scale on the Y axis before you get too excited about the huge bar for a representative image).
Another interesting takeaway here is that having a picture of the actual item may cause it to sell for a bit less than a representative picture. This most likely happens because the representative pictures tend to be very good, while pictures of the actual item tend to be less so.
Let's look at this a different way. How does having a picture change the chances of an item to sell?
The chance of an item selling drops from 86% (any kind of picture) to 62% if there's no picture.
The take home message here is that people may ignore your lot altogether if they aren't sure what it looks like.
These data were collected before the tile view (that has thumbnails of the lot) was added. I expect this divide to grow even further now that you can see a picture without even needing to click on the lot.