If you want to post an image to a blog or forum and SmugMug's standard image sizes won't do, you can make your own.

How to change the image sizes

First, get the URL of your photo. Note that SmugMug's standard URLs contain a size abbreviation after and right before the filename.

Examples:

... /L/birthday-cake-L.jpg
... /X2/house-X2.gif

To create a link to the Original 

Take this example image link:  

http://cmac.smugmug.com/SmugMug/Support-Heroes-painted-faces/i-99kRCRg/4/X3/IMG_0292-X3.jpg

And change it to this:

http://cmac.smugmug.com/SmugMug/Support-Heroes-painted-faces/i-99kRCRg/4/O/IMG_0292-O.jpg

That will give you the Original image size.

To create custom sizes

You can replace those letters in both parts of the URL with the Width x Height you want.

Examples:

... /1000x667/castle-1000x667.jpg
... /640x480/house-640x480.gif
... /200x300/img_3421-200x300.jpg

This example image is 2277x2038.  But we want to show it as 1000X1000 so we change the link like this.    

http://cmac.smugmug.com/SmugMug/Support-Heroes-painted-faces/i-99kRCRg/4/1000x1000!/IMG_0292-1000x1000!.jpg

No calculators or headaches

We won't change the aspect ratio of your image because that would distort it. Suppose your image is 600x400 pixels. That's a 3:2 aspect ratio. So if you specify 1200x600, which is a 2:1 ratio, we will pick 900x600 so it looks perfect.

Tip: You can avoid doing math and just put in something like 1000x1000. The longest dimension will be made 1000 pixels in
size and the other will be scaled according to the aspect ratio of the image.

This feature respects the file extension. For example, if you
upload a PNG, you can now get any custom pixel resolution you want, and also choose whether you want a JPEG or a PNG based on the extension in the URL.

We'll only render an image as large as your largest allowable display size. That may be the dimensions of the original image,
or it may be smaller if you've blocked some of the larger display sizes.