I have quite a few photos, some of which I consider to be particularly good. I've been thinking of putting some up on stock photo sites (that's another discussion), but have been wondering about image quality.
Are there any important aspects a photo should have before being put up on a stock site? I'm thinking of subject, composition, colour, and clarity, but what else?
One thing that's not technical but more subjective is how "sellable" the image is. The world has so many photos of sunsets, women sitting at desks on the phone, and nice forest landscapes that you will want to choose subjects that are something a little different in order to stand out amongst the crowd.
Yes, technical correctness will be needed, but to really get noticed on a stock site (and in some cases, to get accepted) you need images that are timely and can't be found in hundreds of other locations.
As you noted, subject and composition are vital.
Another item to think about is the mood. Mood is important for a company that is looking for marketing material.
Beyond image quality, be sure to keep in mind that you will most likely need and subjects to sign off on images you sell.
Remember the business side of this. Generally, logos and any identifying information will not be appropriate for a stock photo. A picture of a mug or something that has a Starbucks logo on it won't pass muster.
Also, "identifiable" (yes, it's a little subjective) people need to have model releases. Specific, identifiable, property might need a property release - think of commercial real estate. Maybe you're got an awesome picture of the Empire State building - it might need a property release.
Think about it from the point of view that your photo might be used for anything from hawking anti-depressants to advertising handguns. Some people (and property owners) might not want to have their images (or images of their property) associated with specific causes.
The criteria for technical correctness are listed here: What are the criteria to decide whether a photo is "technically correct" or not?
For me there are more important considerations though. I'd ask myself if "photography is a creative entertainment or source of income for me?". Once you start selling your images, you'll optimize your images for selling and thus limiting your creative freedom that you have as an amateur.
I would say "following the good-photo guidelines" would be the biggy, whilst keeping post-processing to a minimum.
Rule of thirds for framing, good white balance, lighting and exposure, sharpness and contrast, etc would need to be of a high standard. Post processing would really only be used to correct minor issues such as touching up levels and colour balance as far as I would say.
I suppose composition would be a somewhat subjective element, except for objective shots like textures. You would need to find subjects and shots that you find appealing as well as branching out and finding shots that you think may be useful to other people and prospective customers.
For example, a podiatry company would be interested in shots of people walking happily on a beach or walkway with joggers. A sportswear company would be interested in people playing sports (obviously), partaking in exercise activities, leasurely outdoor activities etc.
