Photos are larger than they’ve been in years: page wall posts and news feeds show images in sizes not seen since the early days of Facebook.

That’s a smart move for Facebook, given how photos, especially with tagging, have helped drive the growth of the social network.

And with the impending rollout of the new timeline profile, plus the supersized cover images that come along with it, photo uploading to Facebook will not slip in popularity anytime soon.

Here are the top 20 Facebook photo applications, listed by monthly average users, with brief write-ups of the top six (thereafter the user numbers drop precipitously).

1. Picnik, 3,323,186 average monthly users

The most prominent feature of Picnik is its suite of photo-editing tools.

Picnik users can crop, resize, and rotate photos from Facebook, Picasa, Flickr, Photobucket, or hard drives. Plus, you can special effects, fonts, and shapes to images.

2. piZap Photo Editor, 3,252,590

Photo editing is also the forte of piZap, but unlike the more traditional tools of Picnik, the backgrounds of ill-fated social network Myspace come to mind.

Nonetheless, piZap allows users to add existing photos to pre-created backgrounds, with most of them on the loud side. But somehow the app is striking a chord with enough people to place it second, hot on the heels of Picnik.

3. iPhoto Uploader, 2,301,052

No loud, Myspace-type backgrounds here: iPhoto Uploader is a plug-in for Apple’s iPhoto that allows users to upload photos directly to Facebook, complete with captions and tags.

Apple users are an influential bunch, as this app still ranks third, despite the fact that the last update to the app’s Facebook page occurred in April 2010.

4. Photobucket, 1,543,761

Here, the photos are stored on Photobucket’s servers, rather than on Facebook.

So, instead of creating albums within users’ profiles on the social network, those albums are created on Photobucket, accessible via links on users’ Facebook updates.

5. Pixable, 1,169,225

Pixable is neither an uploading nor an editing tool. It curates photos from users’ friends on Facebook, and from the social network overall (from users who opt to make their photos public), based on relevance to the user.

The app also notifies users when they are tagged in new photos on Facebook. The best photos are ranked and sorted using Pixable’s WonderRank technology, which factors in variables including likes, comments, and tags.

6. My Photos, 1,158,420

More than 1.1 million average monthly users can’t be wrong — or can they?

It seems that the only function of My Photos is to randomly display photos from Facebook users’ friends, and we do mean randomly. There doesn’t appear to be any rhyme or reason to the way the app selects which photos to display, but maybe that was the idea in the first place.

Still, we would have never guessed an app with such limited functionality would attract this many users.

Now, here’s the best of the rest, organized based on the number of users.

7. Photo Gallery, 292,978

8. Cartoonize Your Photo, 288,576

9. Photo/Video Uploader, 258,672

10. Facebook Exporter for iPhoto, 139,354

11. SmugMug, 103,480

12. Picasa Uploader, 88,664

13. FBUploader, 20,062

14. PhotoStage, 18,911

15. Bloom, 18,763

16: Chrome Uploader, 13,548

17. Easy Photo Uploader, 12,098

18. LiveUpload, 6,876

19. Fotolink, 4,659

20. Adobe Photo Awesomizer, 1,263

Readers: How many of these Facebook photo apps have you used, and which are your favorites and least favorites?