The best results can be obtained when you upload a file that is fullsize between 90 and 180 DPI. With a lower resolution, you will be able to see pixels. The website will always open files with a maximum of 180 DPI, unless your files are saved with less DPI. The best thing to do is to upload a file that is fullsize 180 DPI.
You can save your file as .jpg. Advised color mode is Adobe sRGB. U can upload files up to 150 MB. The website will indicate what the quality of the uploaded picture is.
Resolution: 180 DPI
Image format: Jpeg
Max. filesize: 150 MB