В метод передаём массив байт изображения. Можно не весь, а первые 50-100 кб.

                        
private Image getThumb(byte[] bt) {

        try {

            if (((bt[0] & 0xFF) == 0xFF) && ((bt[1] & 0xFF) == 0xD8)) {

                int idx = 2;

                int hd = 0;

                int id0 = 0;

                int of0 = 0;

                int id1 = 0;

                int thof = 0;

                int thsz = 0;

                int ed = 0;

                int fld = 0;

 

                byte[] thumb;

                do {// Find the EXIF - 0xFFE1

                    while (bt[idx] == 0xFF) {

                        idx++;

                    }// Found 0xFF, verify the next

                    idx++;

                } while ((bt[idx] & 0xFF) != 0xE1);

                // Increases for the next byte, and discard 2 of length

                idx += 3;

                // EXIF Header size is 6

                hd = idx + 6;

                ed = (bt[hd] << 8) + bt[hd + 1];

                if (ed == 0x4D4D) {

                } else if (ed == 0x4949) {

                    // Gets the IFD0 position. Get from TIFFHeader

                    id0 = hd + ((((bt[hd + 7] & 0xFF) << 24) + (bt[hd + 6] & 0xFF) << 16) + (bt[hd + 5] & 0xFF) << 8) + (bt[hd + 4] & 0xFF);

 

                    // Calculate the Offset to IFD1 position

                    of0 = id0 + 2 + ((((bt[id0 + 1]) << 8) + (bt[id0])) * 12);

                    // Extract the IFD1 position

                    id1 = hd + (((bt[of0 + 3] & 0xFF) << 24) + ((bt[of0 + 2] & 0xFF) << 16) + ((bt[of0 + 1] & 0xFF) << 8) + (bt[of0] & 0xFF));

                }

                // Get the number of fields in IFD1

                fld = ((bt[id1 + 1]) << 8) + (bt[id1]);

 

                for (int i = 0; i < fld; i++) {

                    int index = i * 12 + 2 + id1;

                    // Get the Thumbnail Offset and Thumbnail Size

                    if ((((bt[index + 1]) << 8) + (bt[index])) == 0x0201) {

                        thof = (((bt[index + 11] & 0xFF) << 24) + ((bt[index + 10] & 0xFF) << 16) + ((bt[index + 9] & 0xFF) << 8) + (bt[index + 8] & 0xFF));

                    } else if ((((bt[index + 1]) << 8) + (bt[index])) == 0x0202) {

                        thsz = (((bt[index + 11] & 0xFF) << 24) + ((bt[index + 10] & 0xFF) << 16) + ((bt[index + 9] & 0xFF) << 8) + (bt[index + 8] & 0xFF));

                    }

                }

 

                // Get the thumbnail from the Offset and Size and return it

                thumb = new byte[thsz];

                for (int i = 0; i < thsz; i++) {

                    thumb[i] = bt[(idx + 6 + thof + i)];

                }

                return Image.createImage(thumb, 0, thsz);

            }

        } catch (Exception ex) {

            ex.printStackTrace();

        }

 

        return null;

    }