So that you have the info all in one place:

Photo Fader images: 410 x 205 pixels

Sponsor Fader/Rotator images: 150 x 90 pixels (For other side column images, they should be no more than 150 pixels wide.)

Images for regular photo albums: whatever you'd like, although you'll probably find that anything much wider than 600-700 pixels is going to seem too big. Anything taller than 600-700 pixels is going to require your viewer to scroll down/up to see it all.

Images for articles: Usually around 250 x 350 works well (or 350 x 250 if it's a landscape image.) Be sure to look at your image at least once in preview, though, to see if it's really the size you want it to be. You will typically want it large enough that it doesn't look like a small thumbnail image on the page but not so large that it dominates the article page.

Also, if you need a refresher on how to resize images using Picnik, please go to your magnet.help admin menu and do a Keyword search for "Picnik. You'll want to watch the following videos:  "Editing Images with Picnik.com" and "Using Picnik to resize fader images."