Compression

• If you have saved your images in a lossy format such as JPEG, you may have accidentally applied a too-high compression factor. Compressing images keeps the file size low at the cost of quality; images that are compressed too much may display compression artifacts or look fuzzy.
  
  

Wrong File Format

• Certain image formats, such as GIF, only allow for a very limited palette of colors. Although these formats are suitable for images with a small amount of colors, such as black-and-white drawings, using them for photographs will result in a loss of color information and visible pixelation in the image. Ensure you always use the appropriate image format to avoid this issue.
  
  

Small Images Resized Upwards

• Avoid resizing small images to be larger, whether you do so in an image editing program or by altering the image's dimensions in your blog post. Doing so will lead to the image looking blurry and fuzzy, as if viewed through a magnifying glass.
  
  

Fixing Issues

• If you have access to the original images, open them in your favorite image editing program and save them again using a higher quality, larger size and correct format. If you obtained the images from another website, you may be unable to find a higher-quality version of them; in this case, simply replace them with a different image. Some image hosting services may automatically compress your images or switch them to a different format to enforce file size limitations; examine your host's terms of service and switch to a different hosting service if necessary.