Store the images in S3. The DynamoDB limitations have been described by willglynn. However you may want to store the urls to the images and other metadata in your DynamoDB.
A bit of warning about DynamoDB, it can be very expensive. Going up from free-tier may easily cost a few hundred dollars for a dozen more throughput units. If you used it for storing large items (close to 64KB such as images) which need even larger capacity, it's very likely you would end up paying thousand of dollars. For storing metadata with AWS, you may want to check SimpleDB.
