Preserve white space when hiding textbox in rdlc file

To prevent the behaviour that you are seeing, you can place some other object (like rectangle or a line) onto your designer in the same location as your image and have it take up the same horizontal space as the image on the left.

When the image is hidden, this object will remain there and prevent the right side textbox from moving.

I would keep this object visible in the designer and set its colour to match your background colour (e.g., White) during runtime so that you don't see it.

I would also give it some descriptive name like LineWhichPreventsTextBoxFromMovingWhenImageIsHidden so that some future maintainer of the report does not inadvertently remove it and thus cause a breaking change.