Given that cameras are now ubiquitous — with most people carrying a smartphone in their pocket — it’s common for users to photograph their paper drawings when they wish to convert them to CAD.
The truth is, photographing paper drawings (or any other flat object) is a poor choice when it comes to CAD conversion.
You should always scan your drawing using a paper scanner.
Let’s look at the common problems that arise when photographing a paper drawing.
Problem: Photos Are Skewed (The Parallax Problem)
In simple terms, parallax refers to the apparent distortion in measurement when an object is observed (or in this case, photographed) from different angles.
Because of this unavoidable limitation, it’s effectively impossible to capture a perfectly accurate photograph of your drawing. The result will be distorted dimensions, inconsistent line widths, and inaccurate proportions for objects or text.
A scanner completely avoids this problem by using a moving camera that remains perfectly parallel to every part of the paper as it scans.
Problem: Photos Are Not Isolated
A scanner captures your drawing in a controlled lightbox environment. There are no background objects, shadows, or textures included — just the drawing itself.
By contrast, a photograph includes everything in the camera’s field of view — the table, the floor, shadows, or even your shoes — unless you spend time manually cropping and cleaning the image.
Problem: Photos Are Heavily Compressed
This might seem counterintuitive because smartphone cameras improve every year.
I use an iPhone myself and am constantly impressed by the image quality — but that doesn’t make it suitable for scanning drawings.
The JPEG (JPG) file format was developed specifically for digital photography. It allows people to store thousands of images by applying heavy compression, which inevitably reduces image fidelity.
That’s perfectly fine for portraits, landscapes, or food photos — but terrible for technical drawings.
While most modern phones offer higher-quality image formats, including RAW, these are still not ideal for CAD conversion.
By contrast, scanners allow you to save images in lossless, monochrome TIFF format — the ideal standard for drawing conversion.
Problem: Photos Have Unsuitable Lighting
A scanner uses a moving light bar that evenly illuminates the entire surface of the drawing.
This eliminates shadows, glare, and uneven brightness.
Even with careful setup, a photographed drawing will almost always suffer from inconsistent lighting — areas that are too dark, reflections, or shadows from your hand or phone. These variations make the image harder to interpret and process accurately during conversion.
Which Scanner Do You Recommend?
We don’t recommend specific scanner models. Scanner technology has remained largely unchanged for about 30 years.
Even a standard printer–scanner combination, like those found in most home offices, will work perfectly well.
The only real consideration is choosing a scanner large enough for your paper size.
But What About a “Scanner” App on My Phone?
Many smartphones, including iPhones, now offer so-called scanner apps — but these are not true scanners.
They simply apply digital corrections and filters to a photograph of your drawing. This doesn’t solve the problems described above.
At best, you’ll still face parallax distortion and lighting inconsistencies. In most cases, the resulting image will be unsuitable for accurate CAD conversion.
Summary
If you plan to convert a paper drawing to CAD, always scan — never photograph.
Scanning ensures dimensional accuracy, consistent lighting, and high-quality, lossless image data — all essential for a clean and precise conversion.
