Nowadays it looks everyone is a gamer of some sort, and the casual gamer is probably the fastest growing population among them. The reason this is happening is because there seems to be more and more games being developed that cater to all sorts of demographics. When this happens, niches are formed, and a recent niche that has come to light is that of Hidden Object Games and / or Difference Games.
The origins of this niche date back a few decades ago when these types of games where introduced in heavily illustrated books. People of all ages would test their skills at searching for specific items or people in a crowded landscape full of all sorts of crazy characters who were in the middle of some sort of chaotic episode. Since then, this pastime has turned to children as its main audience with merchandisers filling the shelves of bookstores with "find it" books featuring just about any popular character from children's favorite movies or TV shows. However, now we are in the era of online gambling where virtually anything is possible, and adults (especially middle aged women) are back in the hunt for Hidden Object Games that feature content interest them particularly.
Today's Hidden Object Games target these casual players who like to spend their free time with their computers relaxing with something a little girly with music that soothes. The content typically includes quiet or mysterious places that you search for antiques or other relics. These places could be libraries, attics, ancient ruins, gardens, forests, or worlds of make believe. You then have a list of things to find, and once you find them, you click on them to take them off the list. The characters often need to find certain items to escape a maze or search out clues to solve a mystery or crime of some sort.
Difference Games are mentioned above as being the same or at least very similar to Hidden Object Games. The goal here is to look at two very detailed pictures side by side and search each to see what makes them distinct from one another. They can be paintings, illustrations, or what appears to be simple greeting cards. The player is usually being timed as they scour the screen for a certain number of differences. Some have the player follow a storyline as they go from screen to screen to keep it interesting as though they were actually accomplishing something by finding the variants.
The above argument that this niche is made up of mostly middle aged women can be backed up by the majority of the content of these games. While there are exceptions to these kinds of themes, most emphasize romance, country homes, shopping malls, fantasy, and adventurous, heroic women. If another demographic had been targeted here, the exceptions of violence, suspense, and slapstick humor would have been more prevalent by far.
So one could surmise that Difference Games are a subcategory of Hidden Object Games niche. At any rate, if you find what you've just read interesting and you'd like to try your hand at some of these games, feel free to hop on your favorite search engine and find out what you've been missing!