Getting so frustrated with this. All I want is the same function as the Windows resize power tool.
i.e. select 1 or more images in finder - right click - resize - select 1 of preset sizes. Job done.
Launching in preview or any other application is more long winded. Mac is slick but so far complete fail on this task
Steps:
1. Select multiple pictures in Finder.
2. Open in Preview.
3. Observe the right-hand column showing all pictures.
4. Observe the top picture is selected.
5. From "Edit" menu, choose "Select All".
6. Observe that all pictures in right-hand column are selected.
7. From Tools menu, choose "Adjust Size...".
8. Proceed to adjust the size as described in earlier posts.
9. Observe that size changes are applied to all pictures.
10. Save your work.
In step 1, you may need to have all pictures with the same orientation: landscape or portrait.
In step 5, command-A is a shortcut for "Select All".
In step 8, the dialog that appears for "Adjust Size..." has a "Fit into" popup from which you can choose any of several preset sizes.
These steps are written for Preview.app from OS version 10.5 Leopard or 10.6 Snow Leopard. They may work on 10.7 Lion. They
do not work on 10.4 Tiger (Preview lacks "Adjust Size..." tool).
If you always resize images to the same fixed size, then the simplest long-term solution will be making an Automator workflow. You then drag and drop your images on it. Fortunately, the entire resizing can be done in one Automator action, so it's going to be a brief and simple workflow. You should even be able to find an existing example by googling terms like
Automator resize images.