如何使用PHP计算出两个图像的相似度

there are two jpg files binary data,how to work out their degree of similarity using php. if it is possible to get color infomation from binary code.what's more ,the server cant surport gd,it's a delegate server.

These previous questions seem to be related:

• How can I measure the similarity between two images?
• Image fingerprint to compare similarity of many images
• What algorithm could be used to identify if images are the "same" or similar, regardless of size?
• Duplicate image detection algorithms?
• Similar image search software (like TinEye)
• Looking for image similarity library that doesn't care about image dimensions