Printing photos from my iPhone?

Can i print photos from iphone 4s for canon selphy CP740? I keep trying and it never works!

You have not specified how you try to transfer the picture file between the two. USB cable? Data card? Wireless?
"The Canon Selphy CP740 gives you a choice of printing methods. You can print directly off a memory card, from an attached PictBridge or DPOF camera, wirelessly from a Bluetooth device (you'll need to purchase the optional Bluetooth adapter), or from your PC" http://techtaxi.blogspot.com/2007/10/canon-selphy-cp740-photo-printer-review.html
Do you have that? What does the user manual say to do? (it is on the disk)
Did you try putting into computer, then printing?

It would be best to either taking out your memory card from your IPhone and inserting it into the printer. Or by uploading the pictures to a computer(prefer Mac computer since its IPhone) the print from there.

You can indeedy!
you will find a lot of people asking the same thing
first of all, is your printer Airprint compatible? If you aren't sure, have a look at the list of apple aiprint enabled printers here:
http://support.apple.com/.../kb/ht4356

if the printer is not listed, a further option is to have a look in the itunes app store for a printing app, personally i favour print n share