Milo Design

As of today, July 1st, the picture quality policy announced in February, 2012, fully takes effect. Product photos uploaded with your listing must be at least 500 pixels on the longest size.

The "but"...your GTC (Good Til Cancelled) listings with smaller photos are exempt - UNTIL you revise the listings or end and restart 'em.

Picture Quality Policy

The main points in the policy include:

All photos must be at least 500 pixels on the longest side of the picture.
Photos cannot have borders.
Photos cannot have seller-added text or seller-added artwork.
Your watermark should be no bigger than 5% of the total image area, have an opacity of no more than 50%, and never obscure the item.
When you list a used item outside of books, movies, music, and video games, you cannot use the eBay catalog stock photo in the primary photo position. You must upload your own photo.
You must upload at least one photo per listing.

Best Practices

Take your photos against a solid background - white is generally best, though black, gray or another color that complements and contrasts with your item may work well.
Use as many photos of your item as you can, up to 12. Show different views, show enlarged detail and definitely show any flaws or damage. (You may draw a simple arrow or circle on photos to point to such damage.)
Use large photos up to 1600 pixels so shoppers can see all the details.
Use eBay Pictures Service for your photos. eBay-hosted photos are much nicer than they used to be - and when your photos are hosted by eBay, they will appear at the top of your listing in the "title bar" and will be easily viewed by those shopping from their smart phones or tablets.

eBay has a very good photo-taking guide here. Please take a few moments to review it. By the way, if you have questions about taking photos, you may ask for advice at eBay's Photos and HTML discussion board.