In a previous post I talked about what kind of photos you should upload and what sells, here is the flip side to that. Knowing what doesn't sell is just as important as knowing what does.
A lot of what is on this list is only on the list because there is so much of it out there already, not because they are low interest subjects.
*Disclaimer: I put this list together based on my own experience, just because something is on this list in no way means it wont sell.
Photos taken at the zoo - Taking photos at the zoo can be great practice, but unless you can make the shot look like it was taken in the wild these have low sales potential.
Flowers - Unless they are magazine quality with the name of the flower don't even bother.
Clouds - Everybody takes cloud photos. I actually take them to use later if I need to replace a dull gray sky in a landscape or something. Unless they are really good they are not worth the time to submit.
Sunsets/Sunrises - This is another one that there are nothing wrong with them, they just have to be really good to stand out against all the ones that are for sale already. Make sure those horizon lines are straight if you are going to submit them!
Snapshots - Snapshot is a broad term basically meaning unprofessional looking or unappealing. If it looks like a five year old could have taken it, its probably in this category.
Photos taken with on-camera flash - Using the flash that is built into your camera is probably the worst thing you can do to a photo. Do yourself a favor and get that flash off your camera! This should be required reading for all photographers www.strobist.blogspot.com
Photos with poor composition - Cropping or cutting off part of your subject. If your taking a portrait try to keep all of the models head in the frame. When someone buys your photo they can always crop it down, but they cant "uncrop" (think I just made up a word).
Under or overexposed photos - Try to avoid taking photos where there are blown out areas or the overall photo is too dark. Keep an eye on your light meter and histogram on your camera when shooting.
Copyright infringement - This can be really frustrating and I still have a hard time with it. Be careful of what you take photos of or what might be in the background of a photo you take. Don't take photos with visible logos or brand names, photos that you didn't take, photos with license plates or identifying marks on vehicles, photos with artwork in them that is not your own. The list goes on, and on, and on some more. iStockphoto.com has a useful wiki where you can get more info on things that are protected by copyright here.
Similar photos - Try not to submit too many similar photos. Giving buyers a variety is great, but try to make shots from a series different enough so it not just a model changing her expression slightly for 100+ photos (for example). Try to go for quality not quantity. Having 100 great unique photos in your portfolio is better than having 500 really similar not so great photos.
Photos with technical flaws - Blurriness, graininess, purple fringing etc. Be sure to check your photos at at least 100% before submitting.
Landscapes/nature photos - This is another one that if done right will most likely sell, but there are so many of this type of photo out there yours will have to be pretty awesome to get noticed.
As long as this list is I have only started to scratch the surface.
For the record I am guilty of submitting and selling photos of all these things. I'm not proud of it, but I have learned a lot by getting it wrong the first time. Also there are always exceptions to the rule. What I'm talking about here is really knowing what your doing and doing it wrong on purpose for artistic effect, not doing it wrong on accident.
Hope this helps!
If you have any comments or questions please email me.