What is the background of the picture of the fruit falling into the water?

You can PS, but it's troublesome. You can buy gradient background paper on Taobao, which is not expensive.

But the picture on your left is mainly light. Just use a flash and add a reflector. The key is the angle of lighting. You should try more and don't reflect light on the picture.

After lighting, the water drops will be more obvious and the picture will be more transparent. Flash is necessary to photograph the fruit falling into the water.

You can use magazines or something, but the main problem is that if your background picture is a little messy, it should be fuzzy enough, otherwise the background will be messy. The picture on the left should also polish the background. The one you shot is too messy.

Just use solid paper, but don't reflect light, because you want the background polished.