What makes an image too small?
An image needs to be sized based on the media. Print resources generally need images at 300 dpi. Web and video images are 72 dpi. A web image which has 72 "dots" (or pixels) every inch, when used in print, needs to be reduced in size until there are there are 300 "dots" for every inch: about 24% of the web sized image. While a 72dpi web image looks fine on screen, it will pixelize when printed.
What's the difference between a vector (Illustrator) eps and a raster (Photoshop) eps or jpeg?
Vector images use mathematical formulas for curves. No matter how large the image is made, the vectors apply the same math, and the curves stay smooth. For this reason, an original logo image is always created with vector-based software, most commonly Adobe Illustrator. In the example below, the shapes are shown as original vector mages, and then as jpeg (bitmap Photoshop) images at several resolutions. Even high resolutions of raster-based art have some "stair-stepping" effect along curves or diagonals.
Help center provides clear and concise information on photo resolutions.
Raster and Vector Graphics shows the difference between a vector eps and a photoshop (rasterized) eps.
Wikipedia article on image resolution also has additional lnks for more information.
If you have suggestions for links on image resolution, please contact us.