Solution 1:

Use this Method. This will return list all the images path inside your sdcard, and if you don't want any specified image extension you can filter that out.

public ArrayList<String> getFilePaths()
    {


        Uri u = MediaStore.Images.Media.EXTERNAL_CONTENT_URI; 
        String[] projection = {MediaStore.Images.ImageColumns.DATA}; 
        Cursor c = null;
        SortedSet<String> dirList = new TreeSet<String>();
        ArrayList<String> resultIAV = new ArrayList<String>();

         String[] directories = null; 
        if (u != null) 
        { 
            c = managedQuery(u, projection, null, null, null); 
        } 

        if ((c != null) && (c.moveToFirst())) 
        { 
            do 
            {
                String tempDir = c.getString(0);
                tempDir = tempDir.substring(0, tempDir.lastIndexOf("/"));
                try{
                    dirList.add(tempDir);
                }
                catch(Exception e)
                {

                }
            } 
            while (c.moveToNext());
            directories = new String[dirList.size()];
            dirList.toArray(directories);

        }

        for(int i=0;i<dirList.size();i++)
        {
            File imageDir = new File(directories[i]);
            File[] imageList = imageDir.listFiles();
            if(imageList == null)
                continue;
            for (File imagePath : imageList) { 
                try {

                        if(imagePath.isDirectory())
                        {
                            imageList = imagePath.listFiles();

                        }
                        if ( imagePath.getName().contains(".jpg")|| imagePath.getName().contains(".JPG")  
                                || imagePath.getName().contains(".jpeg")|| imagePath.getName().contains(".JPEG")                                    
                                || imagePath.getName().contains(".png") || imagePath.getName().contains(".PNG")
                                || imagePath.getName().contains(".gif") || imagePath.getName().contains(".GIF")
                                || imagePath.getName().contains(".bmp") || imagePath.getName().contains(".BMP")                         
        )
                        {



                            String path= imagePath.getAbsolutePath();
                        resultIAV.add(path);

                        }
                    }
            //  }
            catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }

        return resultIAV;


    }