Open Clipart Library - Enchanting Graphics
This project aims to create an archive of clip art that can be used for free for any use. Public Domain Graphics as is the Creative Commons.
Use jpg format for photographs and png format for clipart. png has transparency too.
Web Graphics Notes: GIF, JPEG or PNG
PNG images always look great and they usually achieve very respectable compression ratios. PNG protects you from the reduction in image quality found with JPEG
What is the difference between JPEG, GIF and PNG?
JPEG is a standardised image compression mechanism. JPEG is designed for compressing either full-colour (24 bit) or grey-scale digital images of "natural" (real-world) scenes.
It works well on photographs, naturalistic artwork, and similar material; not so well on lettering, simple cartoons, or black-and-white line drawings.
Bitmap Vs Vector
A BITMAP (somtimes called raster) uses a set of PIXELS on a FIXED grid (map) to define an image. Hence, the term bitmap.
A VECTOR uses a set of POINTS based on a FORMULA that is used to define an image (its strokes and fill colors).
IrfanView is suitable and exhaustive for most graphics optimization and conversion for the webmaster or coder. This is a must-have for any computer user. This can make a transparent gif too.
XnView can make easily make a transparent gif and png. this also very useful for managing your graphics.
GIMP - Versatile Graphics Manipulation Package
GIMP is the GNU Image Manipulation Program. It is a freely distributed piece of software for such tasks as photo retouching, image composition and image authoring. It works on many operating systems, in many languages.
Inkscape - Vector Drawing Graphics SVG PNG:
Inkscape is an Open Source vector graphics editor, with capabilities similar to Illustrator, Freehand, CorelDraw, or Xara X using the W3C standard Scalable Vector Graphics (SVG) file format.