What do you do when you need to quickly modify an image for a business document or presentation, and you don’t have access to your regular photo editing application or, even more commonly, your Photoshop guy. (Ours is called Rodrigo. Hi, Rodrigo!)

I found myself in this situation the other day, helping a family member with a new business blog. Using an unfamiliar machine, I needed an easy way to crop, resize, and correct a header image for the site, but I didn’t want to spend the time to download and install a photo editor.

Luckily, I remembered a recent post on the TechCrunch blog about online photo editing tools. I was skeptical, being a pretty big Photoshop snob, but it was worth a shot. Picnik.com was the domain I remembered, so I tried it and was really happy with how quick and easy it was.

Picnik is not Photoshop, nor does it try to be, and that’s part of its appeal. Let’s face it, an awful lot of photo editing comes down to a handful of relatively simple use cases — resizing, cropping, fixing redeye problems, correcting colors, and so on. This online photo editor has these tasks down cold. The interface is quick, intuitive, and even pretty enough to please a finicky designer.

Here’s a screen shot of the cropping tool:

I’ve used Picnik several times now, even when working on machines with photo editors installed. It’s quick, it’s accessible anywhere, and it doesn’t hog system resources. It’s even got some hassle-free integration tools that make it easy to edit photos that you have stored on Flickr, Picasa, or other photo sharing sites.

Picnik.com. It’s worth a look. Or at least a mental note in case you end up with an unexpected need.