First, whether you're creating a 50th anniversary slide show for your parents' surprise party or a birthday photo slideshow for your husband, your slideshow will be more successful if you aim to please the subject. The most important thing to keep in mind is that you are selecting music that is appropriate for the slideshow – not your own music favorites. This results in the most meaningful slideshow for your guest of honor, and best captures the person's personality.

The music sets the mood for your slideshow. Pop, rock, swing, or a song with a faster beat conveys fun, excitement, and good times. Ballads or slower songs provide a more emotional connection, and are effective for strong relationships of all kinds. Keep in mind that photos set to a a fast-paced song will be onscreen for a shorter time than photos paired with a slow song.

Some methods for choosing the best music:

Music Genre
What kinds of music does the person or couple like best? For example: pop/rock, country, oldies, R&B, classical, easy listening, jazz, blues, Broadway, Christian/Gospel, Latin music. Don't know? Check out their CD/tape collection or iPod, or see what radio station is on their stereo or car radio. Or ask a close family member or friend. And don't forget that the person or couple may have a favorite performer or band that you may wish to include.

Favorite Song
Does your person have a favorite song? (Or two or three?) Can you work it into the slideshow? The person will be touched and the segment will likely be his or her favorite! Ask close family and friends if you don't know the song. Or develop a ruse and ask the person outright: "I'm putting together a mix CD for the family and want to include everyone's favorite songs. What's yours?" A birthday photo slideshow needs to have the guest of honor's favorite songs!

Relationship
Is there a song that expresses your feelings for the subject of your show? For instance, any slideshow containing photos your friends can take advantage of all the great "friends" songs out there. There are songs about mothers, songs about fathers...any relationship you can think of!

"Our Song"
Every couple has a song that they consider to be "their song." If they're married, it's usually the song that was used for their first dance. So figuring this out is a snap for a wedding or anniversary slide show, or even a life story video slideshow (which often features the person's wedding). And for a wedding photo montage, just find the list of songs that was made for the DJ at the reception!

Top 40
What songs were hits when the subject was born or growing up? These songs are perfect for a birthday photo slideshow or life story video slideshow, which frequently start with photos of the person's childhood. If the song from the exact birthdate doesn't work, look at other songs that were high on the charts at the time. You can look up the exact birthdate song here: http://www.joshhosler.biz/NumberOneInHistory/SelectMonth.htm

Time Period
Songs that are appropriate for a section of photos dating from a certain time period are always a good choice. For a 50th anniversary slide show, you have at least 50 years of popular music at your disposal! But do your research: don't use 1955's hit "Rock Around the Clock" for photos from the late '60s. People are very sensitive to music and a song paired with the wrong time period is distracting. Billboard and Joel Whitburn's reference books are excellent for tracking down the correct music for a time period:
The Billboard Book of Top 40 Hits (1955–present)
Pop Memories 1890–1954: The History of American Popular Music

Specific Theme
Sometimes, only a very specific song will fit the type of photos you have. For example, maybe you have fifteen photos of your child's Halloween costumes over the years, and you're just drawing a blank on Halloween songs. Google it! Search for terms like "Halloween songs" or "Halloween lyrics" and see what turns up. ("Monster Mash" and "Thriller," in this case.) This also works well for vacation photos, since many vacation spots are featured in a song: "On the Way to Cape May," "California Here I Come," "Route 66," "Moonlight in Vermont." The list is endless.

Ask others
Everyone knows tons of different songs. If you need the perfect song for the cake-cutting reception segment in your wedding photo montage, you might not think of the '60s hit "Sugar Sugar." But your mom might! You'll be surprised what songs turn up when you start asking around.