Vector or Bitmap? The Dilemma
Ok, so you have downloaded a zipped folder from a royalty-free image provider such as istockphoto.com and you may have two files - one ending in .bmp and one ending in .eps. If you click on the .bmp file you can see your image, but the other one may come up with "Windows can't open this file", so you don't go any further. But wait! The vector image format could actually be a much better one for your purposes if you have the right tools to edit it.
More about Vector files
.eps stands for Encapsulated PostScript and can be opened and edited in programs such as Adobe Illustrator or Corel Draw
Other commonly used vector file extensions are:
.SVG (Scalable Vector Graphics) .AI (Adobe Illustrator Graphics) .CDR (CorelDraw Vector Graphics) .WMF (Windows Metafile Format) and .DRW (Vector Drawing file)
Vector files are usually much smaller than Bitmap, and much more easily scalable, so good for your web site or Social Media use.
.bmp (Bitmap) files are more familiar, and more suited to photographic images as they handle complex colours better.
Typical commonly used bitmap file extensions are:
.PSD .JPG, .GIF, and .TIF
Editing your Vector file
To find out if you have software for editing your vector file on your PC, right click on the filename and choose "Open with", and a list of suitable software should come up, If not, surf the Web for "free vector graphics editors 2011" or something similar (be sure to check the date of the article so that you get the latest software).
After that, it's up to you! Some of these image editing packages can be quite complicated, but I'm sure you'll find your way to do the basics of sizing and cropping, and you will be impressed with the superlative quality of your vector image.