diff --git a/pkg/captcha/db.go b/pkg/captcha/db.go
index 5095242..c510864 100644
--- a/pkg/captcha/db.go
+++ b/pkg/captcha/db.go
@@ -25,8 +25,8 @@ func NewID(additionalData string, answer Answer) ID {
 	return ID(base64.RawURLEncoding.EncodeToString(idHash.Sum(nil)))
 }
 
-type ICaptchaDB interface {
-	New(data string) (ICaptcha, ID)
+type CaptchaDB interface {
+	New(data string) (Captcha, ID)
 	SetExpiry(expiry time.Duration)
 	GetExpiry() time.Duration
 	Image(id ID) (*image.Image, error)
@@ -34,15 +34,29 @@ type ICaptchaDB interface {
 	IsSolved(id ID) bool
 }
 
-type CaptchaDB struct {
-	DB       map[ID]ICaptcha
-	ExpireIn time.Duration
+type InMemoryCaptchaDB struct {
 	sync.Mutex
+
+	DB       map[ID]Captcha
+	ExpireIn time.Duration
+}
+
+// New accepts an Captcha instance, generates an ID and store it in a database.
+// `data` string is an additional random data used to generate an ID,
+// e.g. IP-address.
+func (cdb *InMemoryCaptchaDB) New(data string, captcha Captcha) (Captcha, ID) {
+	id := NewID(data, captcha.GetAnswer())
+
+	cdb.Lock()
+	cdb.DB[id] = captcha
+	cdb.Unlock()
+
+	return captcha, id
 }
 
 // SetExpiry stores expire value and starts a goroutine
-// that checks for expired CAPTCHAs every minute.
-func (cdb *CaptchaDB) SetExpiry(expire time.Duration) {
+// that checks for expired CAPTCHAs.
+func (cdb *InMemoryCaptchaDB) SetExpiry(expire time.Duration) {
 	cdb.ExpireIn = expire
 	if expire < expiredScanInterval {
 		expiredScanInterval = expire
@@ -64,32 +78,24 @@ func (cdb *CaptchaDB) SetExpiry(expire time.Duration) {
 	}()
 }
 
-// New accepts an ICaptcha instance, generates an ID and store it in a database.
-// `data` string is an additional random data used to generate an ID,
-// e.g. IP-address.
-func (cdb *CaptchaDB) New(data string, captcha ICaptcha) (ICaptcha, ID) {
-	id := NewID(data, captcha.GetAnswer())
-
-	cdb.Lock()
-	cdb.DB[id] = captcha
-	cdb.Unlock()
-
-	return captcha, id
+// GetExpiry returns time for how long captcha will last.
+func (cdb *InMemoryCaptchaDB) GetExpiry() time.Duration {
+	return cdb.ExpireIn
 }
 
 // Image returns image for a captcha.
-func (cdb *CaptchaDB) Image(id ID, style string) (*image.Image, error) {
+func (cdb *InMemoryCaptchaDB) Image(id ID, style string) (image.Image, error) {
 	cdb.Lock()
 	defer cdb.Unlock()
 	if c, ok := cdb.DB[id]; ok {
-		return c.GetImage(style), nil
+		return c.Image(style), nil
 	}
 	return nil, errorNotFound
 }
 
 // Solve compares given answer with a stored one and if failed
 // deletes a captcha from database.
-func (cdb *CaptchaDB) Solve(id ID, answer Answer) (bool, error) {
+func (cdb *InMemoryCaptchaDB) Solve(id ID, answer Answer) (bool, error) {
 	cdb.Lock()
 	defer cdb.Unlock()
 	if c, ok := cdb.DB[id]; ok {
@@ -104,7 +110,7 @@ func (cdb *CaptchaDB) Solve(id ID, answer Answer) (bool, error) {
 
 // IsSolved checks if captcha was solved and removes it
 // from a database.
-func (cdb *CaptchaDB) IsSolved(id ID) (bool, error) {
+func (cdb *InMemoryCaptchaDB) IsSolved(id ID) (bool, error) {
 	cdb.Lock()
 	defer cdb.Unlock()
 	if c, ok := cdb.DB[id]; ok {
@@ -114,8 +120,3 @@ func (cdb *CaptchaDB) IsSolved(id ID) (bool, error) {
 	}
 	return false, errorNotFound
 }
-
-// GetExpiry returns time for how long captcha will last.
-func (cdb *CaptchaDB) GetExpiry() time.Duration {
-	return cdb.ExpireIn
-}