Always resize and crop your images before you upload them to the CMS. If you don't, the browser will do all the work in resizing images which translates to much longer loading times and frustrated visitors leaving your website in droves! It is also very important to run them through an image optimisation tool prior to upload like TinyPNG or Kraken to further decrease the file size.
- up to 72 ppi
- png, gif or jpg* file formats
Filenames should not include spaces or special characters (i.e. ampersands (&) or percent signs (%), etc.), but underscores (_) and hyphens (-) are OK. In fact, when it comes to underscores and hyphens, hyphens are recommended. This goes for all kinds of files, not just images.
A quick note about ppi: It is perfectly fine to use 10 ppi to keep your file sizes way down as long as the image dimensions are exactly what they should be. There is no visible difference on a computer screen between an image that is 300px x 350px at 72 ppi and one that is 300px x 350px at 10 ppi.