Log on to your Picasa account and go into settings. Go down on the page and you will find a check box that says Allow me to upload photos by email - check this box.
Enter a secret word and you will get your unique mail id. Now all you got to do is to send pics at this email id and thats it. This email id shouldn't be shared with others.
By default, Picasa uploads your pics to the built-in drop box albums, but you can choose your destination by entering the name of an existing album in the subject of your email.
You can attach photos upto a size of 20MB in jpg, gif and png format.