"What is the easiest way to turn a bunch of photos into posters with a simple title/tagline?"
Here's how I do it in iPhoto:
- Select the Photos
- Give them a caption (if you haven't already)
- File > Print
- Choose the Contact Sheet Option
- Change to one photo per page
- The caption is wrong, and it is too small
- Choose Settings (not Print Settings)
- Untick Title, choose comments (this displays the captions you wrote earlier)
- Change the Size of the text, and font if you like...
Slightly fancier is instead to select the images, and choose the create option where you can use a bunch of Apple templates, but instead of paying Apple to print the book at the end just print it as a PDF, then print it yourself. This is probably better for a year end year book than posters, but I'm sure you can make it work for either if you really want to...
If you really insist on something prettier, resize them in Preview, then drag and drop them all into Keynote, they will all be placed on separate slides, choose a theme you like, and then add the text yourself.