in you table you created a Primary key named UserID in both tables. this will not work
each table should have it's own primary key column
There is a difference between a primary key and a foreign key.
A primary key is used as a unique identifier for record.
In the case of the email address "email@example.com", the id column value is 8.
in your image table, you need to have a primary key column that is the unique identifier for the image record, and then also have a UserID column that is numeric. For each image that should be associated with the email address "firstname.lastname@example.org", set the value of the userID column to 8.
you may want to do some research using google on Foreign Keys and Primary Keys.