The "invalid file extension" error message can be extremely frustrating when a user wants to upload an image to a social networking site or an online image host. The file extension serves a fundamental purpose in most operating systems, and is equally important to online applications that allow uploads. Fortunately, there is an easy way to understand the reasons for file extension-related errors and an equally simple solution.
The file extension is the short tag at the end of a file's name. Some commonly encountered extensions are .txt, .pdf, .jpeg and .doc. Because each file comes from some program or another, the file extension helps the operating system decide on how to open it. In this way, the files within a computer remain organized. Not all operating systems use file extensions, however, with the most notable example being Linux. Online services such as image hosts have a specific list of formats with which they can work.
Most Common Image File Extensions
Some image file types are more often used in Web pages and applications than others. For example, the .png file type is widely used for small images on Web pages. The formats most often accepted for upload to social networking sites like Facebook and image hosting sites are .tiff, .gif, and .jpeg. The .jpeg format in particular is preferred by these sites because it is usually smaller than the others.
There are several reasons why a website would not allow some image formats to be uploaded. For instance, some image formats produce high-quality, but very large, images. These types of images would quickly fill a popular website's databases and would strain their servers. Additionally, proprietary image types such as Photoshop's .psd file are not accepted by these sites, because they require special software to open them, whereas other image types do not.
How to Resolve
Websites that accept images for upload usually have a list of accepted file types directly below the "Upload" or "Browse" button. To check the file extension of an image in Windows, the user need only right-click it and then click "Properties." If the image in question is of an incompatible file type, there are several free and commercial software programs that can open a file of one type and convert it to another. Keep in mind that .jpeg is the most widely accepted image format.