JPEG & PNG files aren't quite ready for laser cutting.
Lasers need artwork made up of vector paths rather than pixel based images.
If you can source or export vector design files from your software then that will work out best. We currently use DXF, AI, SVG or EPS files. More about this here.
Here are some other ways to get files.
Alternatively, as a quick fix you can convert simple images to vectors.
How to convert simple images to vector artwork
Make sure your image is a single solid color rather than a line drawing to prevent duplicate cutting lines:
No software (online)
Upload a black and white PNG or JPG to https://convertio.co/
Convert the design to an vector EPS
Download the EPS and upload it into your Ponoko account.
PNG to SVG
Upload a black and white PNG to https://www.pngtosvg.com/
Set the options to 1 color and what ever simplification settings make sense
Download the SVG and upload it into your Ponoko account
Software: Adobe Illustrator (paid software)
Function: Image Trace
Object > Image Trace > Make
Bring up the panel with 'Window > Image trace'.
Select the 'black and white mode'. Expand the 'advanced' section. Then tick the 'Ignore white' box
Object > Image Trace > Expand
Software: Inkscape (free software)
Function: Trace Bitmap
Path > Trace Bitmap > Ok
The original image will still be behind your new traced image, so make sure you select it and delete it