About Locket brooches
Lockets are a very popular form of antique jewellery and vintage jewellery. Normally we think of a locket as a piece of jewellery which hangs around your neck however if you are lucky you can also find antique and vintage brooches which have locket compartments. 

Types of locket brooch:

Mourning Brooches
In Georgian and Victorian times locket brooches were popular for holding a memento of a departed loved one, they were given away with a lock of hair inside.  With mourning brooches the locket compartment is usually at the front of the brooch and the hair can be quite ornately worked into a plait or scroll. This sometimes has gold initials or pearls decorating the hair. Georgian locket brooches are quite small and delicate in comparison to Victorian ones. Just look at the difference in these two examples of locket brooches:

Georgian  Mourning Locket Brooch

Victorian Mourning Locket Brooch

Victorian sweetheart locket brooches
The Victorian Sweetheart locket brooch had the compartment hidden at the back of the brooch. From the front the brooch appears to be a normal piece of jewellery but the lady wearing it knew that there was a secret inside the brooch which only she and her love knew about. Young girls and servants were often forbidden to have boyfriends and so they needed to keep their love a secret. Inside the secret compartment would be a photo, a lock of hair or perhaps a small pressed flower with special meaning.
Here are a couple of examples of Victorian sweetheart locket brooches which both have covered compartments in the back:

Picture locket brooches;

Some locket brooches are specifically meant to hold photographs rather than hair. These tend to have a large display area with little frame. Many of these picture lockets date from around the first world war when a lady would wear a picture of her favourite soldier.
Here is an Edwardian picture locket brooch which could hold a photo in both sides with the picture swivelling so that you can choose which side to display: