Currently, we have no good tool for smooth blending between two pictures, using gradients with transparency. There is a workaround described there:
https://www.youtube.com/watch?v=V_EMlmmsRDU
You draw a rectangle over the picture and fill it with color gradient with transparency. It works fine when you want to fade an edge of a picture over a plain background with a single color.
You can also fade all edges of a picture using effects but the blending radius is limited (a radius slider would be helpful) and it does not help at all when you just want to blend one edge of a picture over another picture.
For this I would suggest a completely new tool that would behave like Transparency tool in Corel DRAW - you could apply gradual (linear) transparency over a picture and set precisely start and end point for gradient. In Corel it looks like this (see the video):
https://learn.corel.com/tips/graphics/interactive-transparency/
This would help a lot with presentations.

Sorry if this feature has already been introduced. If it has, please let me know how to use it.