Short answer: Use S3.
Long answer: DynamoDB limits individual records to 64 KB, so you probably can't use DynamoDB unless your images are tiny anyway.
You mention wanting to read your images in a batch request, but DynamoDB batch requests return up to 100 records or 1 MB -- whichever is less -- so it's not like you can retrieve all your images at once anyway. You could dump everything from DynamoDB by reading a page at a time, which means lots of requests one after another. Not fast.
DynamoDB is lower latency than S3, and it supports configurable throughput. However, S3 supports as much concurrency as you want out of the box. Want to upload 1000 images at once? Go for it! It doesn't matter if each object takes 400 ms to write since you can transmit as many as you want concurrently. Similarly, you can dump everything from S3 by getting a list of everything in the bucket and then retrieving every object in parallel.
Other reasons to use S3:
- HTTP compatibility, so you can point other people or applications straight to the bucket
- Hugely lower storage costs
- Pay per request, not for provisioned throughput (640 KB/s of write capacity in DynamoDB costs $460/month, versus a flat $0.01 per 1000 uploads in S3)
The only situation I can picture where DynamoDB might make sense for image storage is if your images are small, frequently changing, and you're very sensitive to read latency. Other than that, use S3.
