Ghost mannequin software. The best software you can use to achieve this effect is Adobe Photoshop. 

Open the mannequin product photos and create the background layer. Fill the background layer you've created with white color. Don't forget to name all the layers you create. This will keep things organized and you won't get confused mid-editing.

Use a Selection Tool to select the product. You can use any Selection Tool you feel most comfortable working with. Lasso, Marquee, Magnetic Lasso, Magic Wand, Quick Selection – all of them can be used at this stage. Zoom in the image to select the product accurately. If you have taken the pictures against the white background, the mannequin is going to stand out nicely and you will remove it quickly. That's why, white color is the best option for quick ghost mannequin editing.

Use Refine Edge Tool to place the mask on the product. Using this tool is a great invisible mannequin photography technique to achieve the floating effect. Select it from the menu bar and put the mask on the product. If needed, keep re-adjusting it to make sure it looks good.

Open foam board product photos. Now you have to do the exact same thing with foam board images. You may think you don't need these photos, but you cannot complete the ghost mannequin Photoshop illusion without them. So, create the background white layer, select the product carefully, put the mask on it and refine it.

Create one picture. When you've done all the previous steps for both types of photos, you have to merge them together. In order to do that, drag one image on the top of the other one. 

Organize and adjust the layers. Check if the mannequin image is higher than the foam board one. If not, correct that and adjust the layers in a way that makes the edges of the product coincide.
Delete the non-essential parts. Now you need to hide your ghost mannequin layer and remove the unwanted parts. Delete the foam board so that it doesn't stand in the way of the mannequin. Afterwards, you need to make sure that everything is nice and clean. Pay close attention to the neck and shoulders part of the mannequin – they are the most problematic.

Create more depth. Lastly, you need to give the item some depth, so that it looks more realistic. To achieve such effect, add a shadow between two layers and then merge all of them. Next, save the photo as a different file. 

Positioning. All items you take pictures of should be of the same size. They should also be situated strictly in center. The images should line up perfectly. To ensure maximum alignment, create guidelines in a Photoshop template.

Crop the image. Similarly to previous step, crop your photos identically. That means if you crop one photo horizontally, you should cut all the other photos in the same way.
Invisible mannequin photography – better than ghost?
If you don't want to retouch your photos and make a ghost mannequin photography, you may invest money in buying invisible mannequin. Such photography mannequins for sale consist of many parts and each part has a special use, which can better display your clothes. Usually they have 8 parts that can be easily separated. Mostly you will use removable chest and arms, as such parts are always "seen" in terms of regular mannequin photography.

So, keeping these parts invisible, you will help customers more easily imagine themselves wearing the garments. In terms of types of clothing, invisible mannequin photography is quite useful for things like blazers, jeans, jackets and shirts. Their biggest advantage is that they can bring the inside of your clothes to life without the need for Photoshop.