That said, for novices (and there are still a few out there) delving into the world of graphics can be intimidating especially if using an image isn't going to be as straightforward as they hoped. For instance, there are times when a transparent background is required, and while a png may have one, depending on how the artist created the image, a jpg will have a background 100 per cent of the time. Only with vectors, a format that can be altered without any loss of quality, is transparency of background guaranteed.
A cautionary addendum to this, however, is that in order to open a vector file, one does require advanced image editing software, something everyday users might not have at their disposal.
Professional software programs (like Adobe Illustrator and CorelDRAW) are quality products providing tools to work one's own magic on an image. However, they can be rather expensive for hobbyists. The good news though is there are free options online for people for whom such an investment just wouldn't make sense. This link offers some examples: 5 Free Vector Graphics Editors.
For people with simpler needs, or for those who just don't feel quite ready to work with vectors, the popular word is Photoshop. This program is finding its way into households as well as businesses, but with a price tag attached still isn't a practical option for everyone. A great alternative is GIMP which can be downloaded at www.gimp.org
A quick Google search also brings up a number of other free options, some specific to a task. This link (www.mashable.com/2007/10/27/graphics-toolbox/) is for Graphic Toolbox, a fun site that lists 35 free graphics programs.
While it's possible to find clipart that doesn't require editing, with a little work, creativity and imagination you can become an image editing wizard. Be fearless. Have some fun and create a little magic with your favourite image.