Following on from looking at the different types of camera last week this week I want to concentrate on the reasons why an ordinary point and shoot camera will not take a picture of high enough standard to be used as a stock photo.
Before looking at how the different cameras differ from each other I want to start by considering how they dont differ - what bits are the same, or in other words what is a camera. A camera is a light proof box with a hole (aperture) in one side allowing an image to be captured, recorded or displayed from the light entering the hole. Many people have probably made the most basic camera at school in science lessons - the pinhole camera. Take a box, make one side out of tracing paper, put a hole in the side opposite the tracing paper and point the hole towards a light source of a candle or incandescent bulb with a large defined element and an image of the light source will appear on the tracing paper.
Starting from that basic idea most cameras have various bits added to them to improve their capturing and recording of light. There is the shutter - which opens and closes the hole. The isis which controls how big or small the hole is. The lens which uses curved glass to bend the light. Finally there is the bit that captures the light to display or record it - in the basic pin hole camera described it only displays the image but most cameras record the light as an image. This can be done with film - a strip of plastic paper or celluloid coated with a layer of light sensitive crystals as was the case with the first cameras or in this digital age with a sensor which is something that translates light into electronic signals. It is in these extra bits that different types of camera show their real differences.
There are 2 main areas that mean most point and shoot cameras dont produce such high quality images as DLSRs and mirrorless. The first is the physical size of the sensor - not its megapixels, but how large the surface capturing the light is. This where a lot of people get confused - they see their camera has lots of megapixels (a mega pixel is a million pixels) and think more is better but that is not necessarily the case. If the pixels are the individual bits capturing the light then it is not just their number but how big they are and how cramped. Point and shoot cameras (and phones) often have very small sensors maybe less than 5 mm by 4 mm and are typically 6.3 mm x 4.7 mm whereas DSLRs/mirrorless will have at minimum over 22 mm x 14 mm up to 36 mm x 24 mm which is the same physical size as the old 35mm film. Or to put it another way the smallest DSLR sensor captures over 15 times as much information per pixel as does the typical point and shoot. Of course some point and shoot cameras do have much bigger sensors say 13.2 mm x 8.8 mm- but their prices are in the range of DSLR cameras and sensor size is only one part of the equation.
The other area of importance at professional level is the "glass" or lens. This can be divided further into the actual quality of the glass and lens and into the specialization of the lens. A camera lens is usually made of more than one "element" and each element can be made of one or more pieces of glass with precise curvature. The role of the lens is to focus the light - to bend the light passing through it so it all meets precisely at a set point on the sensor (or film). Each piece of glass that bend light can also distort it - the less precise the shaping of the glass the more likely distortion. More elements and more bits of glass in elements contribute towards preventing distortion (up to a certain point. So in a point and shoot there is normally only a couple of elements with only a couple of bits of glass - and the manufacturing tolerances in both shaping of glass and construction of lens might not be quite as tight (the same way the tolerances in your road car are not as tight as the tolerances in an F1 car) In the lenses used by DSLRs there will be more elements, more glass in each element, and the glass will be more precisely shaped and put together.
You then come to specialization of lens - your point and shoot camera has one lens built into through which every picture has to be taken. You may have some element of optical zoom (where the lens changes length to make something larger or smaller in the picture) but that will be limited. If you want to get more of a view into shot you have to move further away. If you want to make something bigger you have to get closer. You may find moving further away stops you seeing detail your may find getting closer is impractical or impossible. One the other hand with DSLRs you can fit and remove lenses according to what you want to take pictures of. You can fit a wide angle lens that takes nearly the whole field of view you see with your eyes - or you can fit a macro lens that makes tiny things visible in detail, or you can fit a telephoto that lets you take a picture of the bird at the top of the tree that looks like you were sitting next to it.
So what does all that mean in terms of image? Below I have used the very clever camera comparsion tool found at https://www.dpreview.com/reviews/image-comparison to show the same image taken with 2 different cameras - the first with a nikon point and shoot and the second with the Nikon DSLR that I use myself. This shows the much finer texture and detail you get with a DSLR - which is what the companies selling stock demand.