Custom picture framing (or custom framing) is an oft used, and sometimes mis-used, loose term that describes the act of putting a frame around a work of art or a photograph.  There are more kinds of custom picture frames than I will go into in this post , but they all basically provide a protective element, as well as a decorative element to the work being framed.  They are not, however, pre-made or "ready made" to standard sizes by an outside source.  These are made in bulk, and the quality is not as high as in a truly custom made frame.  And the internal fit of the artwork can be at risk as well.

A custom frame is fabricated specifically to fit and to correctly enclose a specific work of art.  This means the the frame moulding is cut, joined and mitered to size by hand, the mats or liners if used are also made individually to fit the frame, and the glazing, if used, is selected to treat the specific type of art being framed.

Frame moulding comes in pre-finished lengths that the framer then cuts to size, and miteres the corners while attempting to match the pattern of the moulding in the corners, which is not always possible.  So each corner might appear a bit different from the other if the frame face is not flat, but has a specific texture or decorative pattern applied to it.
  
More expensive and higher end frame mouldings are joined raw and then the decorative elements and finish is applied to them after joining.  In this case, decorative elements, leaf, paint or stain is applied to the frame as a single unit.  Most times this type of frame is hand carved and gilded with a gold or silver leaf, or custom color work applied.  The term "Closed Corner Frame" is applied to this type of frame.

The custom framer also has the experience to help choose which type of mat is to be used if the art is a work on paper or a photograph, or fabric covered liner if the work is a painting where glass is not used.  Mats can be fabric covered also, and can be used over the edge of the art (over matting), or underneath the art (float mat) depending on the appearance desired.  When floating artwork, spacers between the frame moulding and the mat must be used to create an air space so the glass does not touch the surface of the art.  This is particularly important in framing original works such as pastels and watercolors.

A custom framer is also familiar with the proper way to mount specific types of art.  Again information for a more lengthly future post.
 
Another type of frame is used behind the surface of oil paintings and sometimes reproductions on canvas to support them from behind.  This is called a "stretcher" when the corners are adjustable to tension the canvas, and a "strainer" (or streighner) if the corners are solidly joined.  The are many types of these as well, and I will go into more detail in future posts.

So although there are levels of "custom" in a custom made frame, the overriding element is that each material choice and process is specifically chosen by the framer along with the customer to fit the individual piece of art being framed.  This allows for the best quality, appearance and balance of budget for the customer and the art being framed.