A system, comprising: at least one storage device including a set of instructions for medical imaging; and at least one processor in communication with the at least one storage device, wherein when executing the set of instructions, the at least one processor is configured to direct the system to perform operations including: obtaining a first optical image of a target subject that includes a target region to be scanned or treated by a medical device, the first optical image being captured by an image acquisition device before a scan or a treatment of the target region; identifying, from the first optical image, at least one body part boundary and at least one feature point of the target subject using at least one target recognition model, each of the at least one feature point referring to a point in the first optical image that represents a point of interest or a critical point of the target subject; identifying, from the first optical image, an image region corresponding to the target region of the target subject based on the at least one body part boundary and the at least one feature point, wherein at least one first edge of the image region is determined based on the at least one body part boundary, and at least one second edge of the image region is determined based on the at least one feature point; and determining, based on the image region, whether a positioning procedure of the medical device can be started. at least one storage device including a set of instructions for medical imaging; and at least one processor in communication with the at least one storage device, wherein when executing the set of instructions, the at least one processor is configured to direct the system to perform operations including: obtaining a first optical image of a target subject that includes a target region to be scanned or treated by a medical device, the first optical image being captured by an image acquisition device before a scan or a treatment of the target region; identifying, from the first optical image, at least one body part boundary and at least one feature point of the target subject using at least one target recognition model, each of the at least one feature point referring to a point in the first optical image that represents a point of interest or a critical point of the target subject; identifying, from the first optical image, an image region corresponding to the target region of the target subject based on the at least one body part boundary and the at least one feature point, wherein at least one first edge of the image region is determined based on the at least one body part boundary, and at least one second edge of the image region is determined based on the at least one feature point; and determining, based on the image region, whether a positioning procedure of the medical device can be started. obtaining a first optical image of a target subject that includes a target region to be scanned or treated by a medical device, the first optical image being captured by an image acquisition device before a scan or a treatment of the target region; identifying, from the first optical image, at least one body part boundary and at least one feature point of the target subject using at least one target recognition model, each of the at least one feature point referring to a point in the first optical image that represents a point of interest or a critical point of the target subject; identifying, from the first optical image, an image region corresponding to the target region of the target subject based on the at least one body part boundary and the at least one feature point, wherein at least one first edge of the image region is determined based on the at least one body part boundary, and at least one second edge of the image region is determined based on the at least one feature point; and determining, based on the image region, whether a positioning procedure of the medical device can be started.