To repair a picture frame corner, you can use wood glue to reattach the broken pieces together. Clamp the pieces in place until the glue dries, then sand down any rough edges and repaint or refinish the corner to match the rest of the frame.
It would be cheaper to replace the frame unless the current frame is an antique.
In the picture frame on the top right corner of the image
Corner to corner diagonal
There are several types of picture frame corner brackets available for securing and stabilizing artwork. Some common options include L-shaped brackets, T-shaped brackets, and screw-in brackets. These brackets help to reinforce the corners of the frame and prevent warping or damage to the artwork.
Basic math its 45 degrees.....if its 90 degrees and its coming in 45 such as a picture frame, then the degrees left is 45.....
walmart
Tagalog translation of PICTURE FRAME: kuwadro
On the back of picture frame backings are hooks. when you get everything in the picture frame you just take your finger and move the hook under the frame.
A number of picture frames are just glued together, some will have additional 'brads' or 'Panel pins' as they're known in the UK, to hold the frame together. http://www.refinishfurniture.com/picture_frame_corner_repair.htm
To keep a frame from weathering, you'll want to get one that's UVA/UVB coated. Once it's faded it will be impossible to repair.
Picture, Wall, Frame.
A auto body repair shop with a frame machine can repair the frame.