It depends what density of A4 paper you were using.
At above 60 gsm you would see not very much. However at 60 gsm A4 paper is getting thin enough (like tissue paper) to be slightly transparent and so allow an image possibly to be seen. Tissue paper is used as it is thin enough to be transparent enough to see the projected image.
If you were to make your pin hole camera a camera obscura - a box big enough for you to physically get inside - you could use a piece of ordinary 80gsm A4 paper onto which to project the image from the pin hole and view it from the same side as the pin hole: in this case the light does not need to penetrate the paper "screen" to be viewed and so thicker, non-transparent paper can be used. The camera obscura was used in this way with the occupant tracing the image projected onto their paper to create a good drawing of the scene they wanted to draw.
The daguerreotype.
Pin holiday camera light travels in straight lines
2015
A Pinhole camera.
I think a pinhole camera is similar to the human eye because like the pinhole camera when it sees something it reflects the image but it is an inverted image. With the human eye the brain corrects it and turns it the right way up. The pinhole cameras image is not corrected because it does not have a lens.
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aperture
A pinhole camera has special paper put inside of it, absorbing the light making lots of shadows ect.
The cast of The Pinhole Camera - 2008 includes: Miguel Santellic as Uncle Diego Saurez as Bernal
The Pinhole Camera - 2008 was released on: USA: 17 November 2008 (Santa Fe Film Festival)
a small size.