diff --git a/pkg/captcha/inmemdb/inmemdb.go b/pkg/captcha/inmemdb/inmemdb.go
new file mode 100644
index 0000000..400e193
--- /dev/null
+++ b/pkg/captcha/inmemdb/inmemdb.go
@@ -0,0 +1,157 @@
+package inmemdb
+
+import (
+	"image"
+	"justcaptcha/pkg/captcha"
+	"sync"
+	"time"
+)
+
+type InMemoryCaptchaDB struct {
+	sync.Mutex
+
+	db                 map[captcha.ID]captcha.Captcha
+	expiry             time.Duration
+	expiryScanInterval time.Duration
+}
+
+// NewInMemoryCaptchaDB returns an initialised instance of an InMemoryCaptchaDB.
+// An expiry duration is a time for how long CAPTCHA will be valid.
+func NewInMemoryCaptchaDB(expiry time.Duration) *InMemoryCaptchaDB {
+	db := &InMemoryCaptchaDB{
+		db:     make(map[captcha.ID]captcha.Captcha),
+		expiry: expiry}
+
+	if expiry < captcha.DefaultExpiredScanInterval {
+		db.expiryScanInterval = expiry
+	} else {
+		db.expiryScanInterval = captcha.DefaultExpiredScanInterval
+	}
+
+	go db.cleanExpired()
+
+	return db
+}
+
+// New accepts a CAPTHA instance, generates an ID and store it in a database.
+// A data string is an additional random data used to generate an ID,
+// e.g. an IP-address.
+func (imcdb *InMemoryCaptchaDB) New(data string, cptcha captcha.Captcha) (captcha.Captcha, captcha.ID) {
+	id := captcha.NewID(data, cptcha.Answer())
+
+	imcdb.Lock()
+	imcdb.db[id] = cptcha
+	imcdb.Unlock()
+
+	return cptcha, id
+}
+
+// GetExpiry returns time for how long CAPTCHA will last.
+func (imcdb *InMemoryCaptchaDB) GetExpiry() time.Duration {
+	return imcdb.expiry
+}
+
+// SetExpiry changes an expiry duration to a new one.
+func (imcdb *InMemoryCaptchaDB) SetExpiry(expiry time.Duration) {
+	if expiry < captcha.DefaultExpiredScanInterval {
+		imcdb.expiryScanInterval = expiry
+	} else {
+		imcdb.expiryScanInterval = captcha.DefaultExpiredScanInterval
+	}
+}
+
+// Image returns a freshly generated image for a CAPTCHA.
+func (imcdb *InMemoryCaptchaDB) Image(id captcha.ID, style string) (*image.Image, error) {
+	imcdb.Lock()
+	defer imcdb.Unlock()
+	if c, ok := imcdb.db[id]; ok {
+		return c.Image(style), nil
+	}
+	return nil, captcha.ErrorNotFound
+}
+
+// Solve compares given answer with a stored one and if failed
+// deletes a CAPTCHA from database.
+func (imcdb *InMemoryCaptchaDB) Solve(id captcha.ID, answer captcha.Answer) (bool, error) {
+	imcdb.Lock()
+	defer imcdb.Unlock()
+	if c, ok := imcdb.db[id]; ok {
+		ok = c.Solve(answer)
+		if !ok {
+			delete(imcdb.db, id)
+		}
+		return ok, nil
+	}
+	return false, captcha.ErrorNotFound
+}
+
+// IsSolved checks if CAPTCHA was solved and removes it
+// from a database.
+func (imcdb *InMemoryCaptchaDB) IsSolved(id captcha.ID) (bool, error) {
+	imcdb.Lock()
+	defer imcdb.Unlock()
+	if c, ok := imcdb.db[id]; ok {
+		delete(imcdb.db, id)
+		return c.IsSolved(), nil
+	}
+	return false, captcha.ErrorNotFound
+}
+
+// Remove a CAPTCHA from a database.
+func (imcdb *InMemoryCaptchaDB) Remove(id captcha.ID) error {
+	imcdb.Lock()
+	defer imcdb.Unlock()
+	if _, ok := imcdb.db[id]; ok {
+		delete(imcdb.db, id)
+		return nil
+	}
+	return captcha.ErrorNotFound
+}
+
+// cleanExpired removes expired CAPTCHAs in a loop.
+func (imcdb *InMemoryCaptchaDB) cleanExpired() {
+	for {
+		sleepFor := imcdb.expiryScanInterval - (time.Duration(time.Now().Second()) % imcdb.expiryScanInterval)
+		time.Sleep(sleepFor)
+
+		imcdb.Lock()
+		for id, captcha := range imcdb.db {
+			if time.Since(captcha.Expiry()) >= imcdb.expiry {
+				delete(imcdb.db, id)
+			}
+		}
+		imcdb.Unlock()
+	}
+}
+
+// An instance of InMemoryCaptchaDB
+
+var imcdb = NewInMemoryCaptchaDB(captcha.DefaultExpiredScanInterval)
+
+func GetExpiry() time.Duration {
+	return imcdb.GetExpiry()
+}
+
+func SetExpiry(expiry time.Duration) {
+	imcdb.SetExpiry(expiry)
+}
+
+func New(data string, captcha captcha.Captcha) (captcha.Captcha, captcha.ID) {
+	return imcdb.New(data, captcha)
+}
+
+func Image(id captcha.ID, style string) (*image.Image, error) {
+	return imcdb.Image(id, style)
+}
+
+func Solve(id captcha.ID, answer captcha.Answer) (bool, error) {
+	return imcdb.Solve(id, answer)
+}
+
+func IsSolved(id captcha.ID) (bool, error) {
+	return imcdb.IsSolved(id)
+}
+
+func Remove(id captcha.ID) error {
+	return imcdb.Remove(id)
+}