I'm sure no one can give you an exact number.
There are a lot of factors that have an influence on this, e.g.
- Quality of content
- Theme / Topics (Landscape, People...)
- economic situation / financial crisis
...and many more factors
Nobody could tell you for sure. A lot of people are selling a huge amount of images - not just here but across many similar sites. As Mario says above there are many variables and I think it is increasingly difficult to get large payouts for images nowadays. You may get lucky if you have a high quality and unique image that somebody wants for a high value project.
I'm just starting and have uploaded around 300 images to 3 stock sites. In my first month or so I have had 3 downloads from here, 6 from another site and none from the third. My total income is around $7.50.
My portfolio is mainly landscapes and wildlife but my experience seems similar to other contributors based on looking around various fora.
So if my experience is typical I would guess you would need a portfolio of around 40000 images to reach your target - possibly hosted on more than one site.
Tihs is not a game to make big money unless you put a lot of effort in (or get lucky).
It's a question of quantity, that's for sure. So let's look at the numbers: I got around 50 cents per picture for now.
For other sites I get less. around 25 cents per picture.
You would need to sell 2000 pictures/month.With 0.6% of sales/month, this would mean 300k pictures.
Now you need to know, the more sales you generate, the better you will be positioned and the more sales you will generate. So you would need much less pictures. If you are in video and you create some great videos, you cloud earn more.
If you use more than one site, you will upload the same pictures, but sell different ones. This will increase your income. For me, selling pictures in stock is just a pass time. I take pictures I have and upload them. Some make sales others none.But I generally do not shoot for stock. If you want shooting for stock, you need really to plan and to look around what is needed. Christmas is coming, so Christmas themes would be great. I would, however, do Christmas shootings in January and uploading pictures in Q3.
Also: You need different theme shoots like mechanics, nurses, babies, homework, technology, ... 20 to 30 of each, if not more. This will help to boost your sales.