One of the nice features in iPhoto (part of iLife ‘06 ) is the ability to quickly e-mail someone a photo or set of photos. Just select the picture(s) you’d like to send and click the Email button in the toolbar below the photos. You’ll be asked what size image you’d like to send, as well as whether or not to include the titles and comments with the images. Then your e-mail client will launch and you’ll see an open message with the photo(s) attached. (If you’re using an earlier version of iPhoto, Mail will launch, whether or not it’s your primary e-mail client.)
If you only select one image, the subject of your e-mail will be its name—for example, IMG_3563.JPG or boats.JPG. But if you select more than one photo, iPhoto adds a generic subject, such as “4 great iPhotos.” While informative, this is probably not the subject line you’d like to use. Although I don’t know how to make iPhoto ask you for a unique description each time, I can show you how to change the default subject line to better match your personal style. The following method has been tested with iPhoto 5 and 6.
First quit iPhoto, and then navigate to your Applications folder, where iPhoto should reside. (If you’ve customized your installation, go to the directory holding the application). Control click on iPhoto and select Show Package Contents from the pop-up menu, then navigate into Contents -> Resources -> English.lproj. (If you’re running OS X in another language, look inside that folder—for example, French.lproj.) Find the file named Localizable.strings and make a duplicate of it. You can do this by clicking on it once, pressing and holding the Option key, then dragging the file to your Desktop (or another safe location). If all goes well, you won’t have to touch this file again; it’s just for safety’s sake.
In the English.lproj directory, open the Localizable.strings file in your favorite pure text editor—TextEdit (in plain text mode) or Bare Bones’ free Text Wrangler, for instance. (I’ll assume you’re using TextEdit for these instructions.) Type Command-F to bring up the search box, and then type Mail stuff as your search term and click Next. TextEdit will jump to this section of the file:

The line you need to modify is the one that begins MailGenericSubjectFormat
, and it’s immediately below the highlighted “Mail stuff” line. To create your own message, just change the portion of the line that’s in double quotes to whatever you’d like. Here are some examples:
MailGenericSubjectFormat = "Some photos from Rob"; MailGenericSubjectFormat = "Here are %1$d amazing pix"; MailGenericSubjectFormat = "Cool images from our collection";
Notice that if you want to retain the photo count, you need to leave the %1$d
variable alone, as shown in the second example above. Once you’ve entered the phrase you’d like to use, save the file and quit the text editor. Now launch iPhoto, select a few images, click the Email button, fill in the dialog box, and then revel in your new fully-customized subject line.