No matter what kind of search you perform, keep this in mind: iPhoto searches whatever item you’ve selected in the Library list. If you want to search your entire library, be sure to click Events or Photos. To search the last year’s worth of photos, click Last 12 Months. To search for a specific face or place, click Faces or Places, respectively. To search a specific album, click the album. You get it.
Step 1. Click the Search button or press -F.
Step 2. Type something. iPhoto searches photo filenames, event names, titles, descriptions, faces, places, and keywords.
Step 3. To clear a search (displaying everything again), click ...