实现效果图：

拍照前&拍照后（我电脑摄像头挡住的，所以图片是灰色）

1.点击拍照上传功能调取电脑摄像头权限

2.选择允许使用摄像头之后，页面摄像头区域开始显示画面

3.点击拍照按钮，右侧显示拍摄的图片。点击保存即可

完整代码：

我这里写的是一个组件，所以触发调取摄像头事件是从父组件传过来的。也可以直接写一个页面上。

<template>
  <div class="camera-box" style="width: 900px;">
    <el-row :gutter="20">
      <el-col :span="12">
        <div style="text-align: center;font-size: 14px;font-weight: bold;margin-bottom: 10px;">摄像头</div>
        <!-- 这里就是摄像头显示的画面 -->
        <video id="video" width="400" height="300"></video>
        <div class="iCenter" >
          <el-button type='primary' size='small' icon="el-icon-camera" @click="takePhone" style="margin-top: 10px;">拍照</el-button>
        </div>
      </el-col>
      <el-col :span="12">
        <div style="text-align: center;font-size: 14px;font-weight: bold;margin-bottom: 10px;">拍摄效果</div>
        <!-- 这里是点击拍照显示的图片画面 -->
        <canvas id='canvas' width='400' height='300' style="display: block;"></canvas>
        <el-button :loading="loadingbut" icon="el-icon-check" type='primary' size='small' @click="takePhoneUpfile" style="margin-top: 10px;">保存</el-button>
      </el-col>
    </el-row>
</div>
</template>
<script>
  import {putFileAttach} from "@/api/customer/animalinfo";
  export default {
    props:{
      tackPhoto:{//父组件传过来的状态
        type:Boolean,
        default:false
      }
    },
    data() {
      return {
        loadingbut:false,
        preViewVisible: false,
        blobFile: null,
        canvas: null,
        video: null,
        mediaStreamTrack: '',
      }
    },
    watch:{
      tackPhoto:{
        immediate: true,
        handler (newVal) {//监听接收到拍摄状态后，开始调取摄像头权限。如果功能是在一个组件里面，下面步骤可以直接写在自己的触发方法里面
	        if (newVal) {
            var video = document.querySelector('video');
            var text = document.getElementById('text');
            // var mediaStreamTrack;
            
            // 兼容代码
            window.URL = (window.URL || window.webkitURL || window.mozURL || window.msURL);
            
            if (navigator.mediaDevices === undefined) {
            navigator.mediaDevices = {};
            }
            if (navigator.mediaDevices.getUserMedia === undefined) {
            navigator.mediaDevices.getUserMedia = function(constraints) {
              var getUserMedia = navigator.webkitGetUserMedia || navigator.mozGetUserMedia || navigator.msGetUserMedia;
              if (!getUserMedia) {
              return Promise.reject(new Error('getUserMedia is not implemented in this browser'));
              }
              return new Promise(function(resolve, reject) {
              getUserMedia.call(navigator, constraints, resolve, reject);
              });
            }
            } 
            
            //摄像头调用配置
            var mediaOpts = {
            audio: false,
            video: true,
            video: { facingMode: "environment"} // 或者 "user"
            // video: { width: 1280, height: 720 }
            // video: { facingMode: { exact: "environment" } }// 或者 "user"
            }

            let that=this;
            navigator.mediaDevices.getUserMedia(mediaOpts).then(function(stream) {
            that.mediaStreamTrack = stream;
            video = document.querySelector('video');
            if ("srcObject" in video) {
              video.srcObject = stream
            } else {
              video.src = window.URL && window.URL.createObjectURL(stream) || stream
            }
            video.play();
            }).catch(function (err) {
              console.log(err)
            });
          
	      	}
	      },
        deep:true
      },
    },
    mounted() {
      // 摄像头
      this.video = document.getElementById('video');
      //画布
      this.canvas = document.getElementById('canvas')
      
    },
    methods: {
      takePhone() {//点击拍照截图画面
        let that = this;
        that.canvas.getContext('2d').drawImage(this.video, 0, 0, 400, 300) ;
        let dataurl = that.canvas.toDataURL('image/jpeg')
        that.blobFile = that.dataURLtoFile(dataurl, 'camera.jpg');
        that.preViewVisible = true
      },
      takePhoneUpfile() {//保存图片
        this.loadingbut=true;
        let formData = new FormData()
        formData.append('file', this.blobFile);//图片内容
        // 上传图片
        putFileAttach(formData).then(res=>{//后台接口
          this.loadingbut=false;
          this.$emit('picture',res.data.data);
          this.tackPhoto=false;
          this.canvas.getContext('2d').clearRect(0, 0, 400, 300);//清除画布
          // 关闭摄像头
          this.mediaStreamTrack.getVideoTracks().forEach(function (track) {
            track.stop();
           });
        },error=>{
          this.loadingbut=false;
          window.console.log(error);
        });
      },
    }
  }
</script>
<style>
 .camera-box #canvas{
  border: 1px solid #DCDFE6;
  }
</style>