The test GUI of mashape is somehow not works. But please just try by using command line like this:

curl -X POST --include ‘https://semamediadata-image-ocr-v1.p.mashape.com/’ -H ‘X-Mashape-Key: your API keys’ -H ‘Content-Type: multipart/form-data’ -F ‘file=@/Users/haojin/Desktop/IMG_3535.JPG’ -F ‘lang=en’ -F ‘noempty=false’ -F ‘outform=json’ -F ‘uc=True’

It always works for me.