Compare the difference between the two image below, before and after shadow effect was added.
Site That Offer Drop Shadow Effect Tool
This is an online tool that offer a lot of effect which can apply to images, all you just need to do is to upload your image and give it any effect you like from their tool bar. you can upload image from facebook, pisaca, flickr, photobucket, and also directly from your computer, and the maximum image size supported is 50000Kb (50Mb) To add a drop shadow effect to your picture, simply upload your image and click on "Draw" from the toolbar, choose "Add DropShadow" and download your new edited image.
2. Pic Shadow
Pic shadow perform a single function, just upload your image and it will automatically add a shadow effect to your image, and the maximum image size supported is 2000Kb (2Mb). But there are some cases you don't need to use this if you have photoshop, because it already have built-in tool which you can use to add a drop shadow effect to your pictures, but if you are looking for something faster and easier, then consider using this.
That's all, you can bookmark those site for easy usage. keep uploading and enjoy more of drop shadows effect.