When I searched for "vector" I hoped to be able to download in vector format, not raster jpg format. Are your vector images downloadable as vector eps files??
We are working on a solution to your question.
The issue with vector files is that there is far less standardization of file formats with vector files.
Currently, a jpeg file can usually be read by any graphics application so it is a common standard.
With vector art there are far many more variations in the formats that are considered "vector art". It is very likely that an artist could upload an excellent piece of vector artwork that they created in their favorite program and this artwork would be difficult or impossible for the general public to use open or edit.
One solution for this would be for the image/artwork approvers to open all vector artwork and re-save the files in a standard way using the exact same agreed upon format every time.
There are several problems with this approach. One huge issue is the amount of time this would require of the volunteer image approvers.
One other issue is opening and saving the vector artwork may in some cases actually change the way the artwork looks. For example if a piece of vector artwork uses some effect that is only supported when saving a file in a proprietary format even if that format is an eps file. Postscript (eps) is a self describing language. It is very east to create a postscript file that looks fantastic on your screen but will not output on another device or even be able to be opened if you have software that does not understand what is going on with the code inside the eps file.
The only issue I've come across is stock sites using the newest Illustrator to make .eps files. If it's too new... no one has the new program to support it and it needs to be saved down to a more common version (which has issues at times because the lower version doesn't support some of the new bells and whistles) That process is complicated a bit. I've been using Illust. since it was version 2 way back when lol.
This one (http://www.multimedia-stock.com/7727) , for example, if I saved it down to an Illustrator 9 version it wouldn't support the 3d tool use because that didn't exist in version 9.
I currently use CS3 (not CS5) and I haven't had any issues. My work allows us use of Thinkstock, www.adbuilder.com and www.metrocreativeconnection.com. All of these provide .eps files... NO .ai files. I truly haven't had even one issue at all. Also, MultiMedia Stock allows for .eps or .ai files as well... again I haven't had any issues at all.
It would be nice in uploading to upload the .eps file and a FULL .jpg image that the site could read for preview. That way - if by some chance the downloader doesn't have a program to read .eps files, they could still have something acceptable. I've also noticed if I upload something and it goes wrong? Someone will comment within the day letting me know something was off. I usually then fix the glitch and reupload, so I don't know crazy it would need to be to check every vector uploaded.
On occasion people will email and ask for a different version also, which I feel is like asking a photographer for a high resolution. It is a couple minutes of work, but it doesn't happen often. I never mind sending it though. :)
Let me know if there are any questions regarding vectors. I consider myself an expert level with them and Illust. Been using it since 1992 :)