There are websites that allow you to send messages from a computer directly to a mobile phone, one of these services is Textport
Textport works for US carriers but I don't know what country you are in, however there are others available (Pushbullet and Evernote can both do similar things).
Another method that I often use is to email myself a photo from my computer to the email address on my phone (this will work even if it is the same email address that you are sending from and receiving to).
Another method is bluetooth, if you pc has bluetooth you should be able to send a photo to your phone easily.
Lastly you could always connect your phone to your pc and do it that way. The pc will see the phone as a drive and so it should be a simple case of dragging and dropping.