Design Downloads
There are a number of places online where you can find designs. One of my favorite paid sites is Etsy, but there are a number of paid and free sites where you can download them. SVG (Scalable Vector Graphics) are by far my favorite file format due to the ability to scale them without and distortion, but AI, PDF and DXF files are good choices as well. You can also import line art and photos in other popular graphic file formats such as JPG, PNG and BMP.
Free Designs (some may have purchase options).
Paid Designs.
Free Editing Programs.
RemoveBG - Easily remove backgrounds.