Different types of image formats

1. TIFF (also known as TIF), file types ending in .tif

TIFF stands for Tagged Image File Format. TIFF images create very
large file sizes. TIFF images are uncompressed and thus contain a lot
of detailed image data (which is why the files are so big) TIFFs are
also extremely flexible in terms of color (they can be grayscale, or
CMYK for print, or RGB for web) and content (layers, image tags).

TIFF is the most common file type used in photo software (such as
Photoshop), as well as page layout software (such as Quark and
InDesign), again because a TIFF contains a lot of image data.

2. JPEG (also known as JPG), file types ending in .jpg

JPEG stands for Joint Photographic Experts Group, which created this
standard for this type of image formatting. JPEG files are images that
have been compressed to store a lot of information in a small-size
file. Most digital cameras store photos in JPEG format, because then
you can take more photos on one camera card than you can with other
formats.

A JPEG is compressed in a way that loses some of the image detail
during the compression in order to make the file small (and thus
called "lossy" compression).

JPEG files are usually used for photographs on the web, because they
create a small file that is easily loaded on a web page and also looks
good.

JPEG files are bad for line drawings or logos or graphics, as the
compression makes them look "bitmappy" (jagged lines instead of
straight ones).

3. GIF, file types ending in .gif

GIF stands for Graphic Interchange Format. This format compresses
images but, as different from JPEG, the compression is lossless (no
detail is lost in the compression, but the file can't be made as small
as a JPEG).

GIFs also have an extremely limited color range suitable for the web
but not for printing. This format is never used for photography,
because of the limited number of colors. GIFs can also be used for
animations.

4. PNG, file types ending in .png

PNG stands for Portable Network Graphics. It was created as an open
format to replace GIF, because the patent for GIF was owned by one
company and nobody else wanted to pay licensing fees. It also allows
for a full range of color and better compression.

It's used almost exclusively for web images, never for print images.
For photographs, PNG is not as good as JPEG, because it creates a
larger file. But for images with some text, or line art, it's better,
because the images look less "bitmappy."

When you take a screenshot on your Mac, the resulting image is a
PNG–probably because most screenshots are a mix of images and text.

5. Raw image files

Raw image files contain data from a digital camera (usually). The
files are called raw because they haven't been processed and therefore
can't be edited or printed yet. There are a lot of different raw
formats–each camera company often has its own proprietary format.

Raw files usually contain a vast amount of data that is uncompressed.
Because of this, the size of a raw file is extremely large. Usually
they are converted to TIFF before editing and color-correcting.

Most of this info is courtesy of Wikipedia, which is a great place to
read more about all 5 file types.