While researching i found that Wiki Commons could be act as a database to wide no of images but since there are non tags associated with the images and categories the image opt for is highly unreliable (for example in the category "cat" contains several vague images which does not have cat in it instead they are mentioned in the category cat while retrieving images these vague images can also act as correct answer)....so it could create problem for images they have options as. For the solution i figured out three ways to encounter the problem: 1)Use image recognition:To determine the whether a particular image contain object it is looking for (example:if the captcha asks a question to select the cat; the image recognition tool will then determine whether the image given as option contain cat).This image recognition tool can be build with the help of Python with opencv library since Php's GD library is not ideal for image recognition also it is much slower. 2)Use Clip Arts:We can make a database of clip arts of various objects and making a combination of them and asking the questions accordingly for example:we can use clip arts of monkey,cat and tiger make their combinations and ask the user to select the image with tiger and monkey. 3)we can use first five images of a definite category as an options but we will be left with very few options in our hand
In my opinion image recognition is the best possible solution to the problem since it would also help us with annotations as mentioned here and advantage to image recognition can also be that it could act as an important pillar for Wiki commons as i personally fell that its database is not well organized
Your suggestions are highly recommended and welcome. Cheers ~aalekhN